Stop codons

A stop codon is a trinucleotide sequence within a messenger RNA (mRNA) molecule that signals a halt to protein synthesis. The genetic code describes the relationship between the sequence of DNA bases (A, C, G, and T) in a gene and the corresponding protein sequence that it encodes Essentially, a stop codon is a specific cluster of nucleotides that tells protein construction mechanisms to stop chaining amino acids into a polypeptide chain. Stop codons are the bits of information that tell the body Hey! This protein is finished!. Stop codons work by initiating the release of release factors, proteins that. Susan Payne, in Viruses, 2017. Suppression of a stop codon is a process whereby a ribosome fails to terminate protein synthesis at a stop codon. Most eukaryotic genes terminate with multiple stop codons, but if there is a single stop codon, an amino acid can be inserted into the growing polypeptide and translation continues Stop codons (UAA, UAG or UGA) are recognized by release factors which bind into the A-site and use an activated water molecule to hydrolyze the ester linkage between the completed polypeptide and tRNA. In general, this is a highly efficient process, but may be influenced by both the particular stop codon and nucleotide context permiting low. Definition. A stop codon is a genetic code that signals the end of protein manufacturing inside the cell, like a period at the end of a sentence.The three stop codons are nucleotide base triplets that play an important role in intracellular protein synthesis; physiological and/or anatomical changes are possible if a stop codon is in the wrong position on a DNA or RNA strand, or if the code.

Stop Codon - Genome

STOP codons. There are 3 STOP codons in the genetic code - UAG, UAA, and UGA. These codons signal the end of the polypeptide chain during translation. These codons are also known as nonsense. كودون ختامي في علم الجينات (بالإنجليزية: Stop codon)‏ في الشفرة الجينية هو ثلاثية من النوكليوتيدات في الرنا المرسال مهمته إلى توقيف ترجمة المتسلسلة. تتكون البروتينات أساسا من ببتيدات متراصة (بوليببتيدات) وهي مكونة من. Stop codons are essential for the termination of the translation process. If there is no stop codon in the mRNA, then there is the possibility that the Ribosome would synthesise mRNA until the 3′ end of the mRNA is not encountered. At the 3′ end, there is no codon and thus,.

What Is Stop Codon? Science Trend

Stopcodon. Als Stopcodon oder Terminationscodon, auch Nonsense-Codon, wird in der Genetik ein Codon der Ribonukleinsäure (RNA) bezeichnet, für das keine zugehörige tRNA (transfer-RNA) vorliegt und das daher das Ende einer Sequenz von Nukleotiden darstellt, die an Ribosomen in die Sequenz von Aminosäuren eines Polypeptids übersetzt werden. http://www.aklectures.com/lecture/start-and-stop-codonshttps://www.facebook.com/aklecturesThe website organizes the videos into clear and structured chapters.. Stop codons are also known as nonsense codons, or termination codons. This article states all the facts regarding this particular type of codon. A codon is a specific type of genetic code that carries a certain set of rules, with the help of which information is processed and encoded to form genetic material codons identified potential stop codon readthrough of four mammalian genes. Here we use a modified targeted bioinformatic approach to identify a fur-ther three mammalian readthrough candidates. All seven genes were tested experimentally using re-porter constructs transfected into HEK-293T cells. Four displayed efficient stop codon readthrough

How can there be 64 codon combinations but only 20Genetic Code Chart (PDF)

The codons specify which amino acid will be added next during protein synthesis.With some exceptions, a three-nucleotide codon in a nucleic acid sequence specifies a single amino acid. The vast majority of genes are encoded with a single scheme (see the RNA codon table).That scheme is often referred to as the canonical or standard genetic code, or simply the genetic code, though variant codes. However, despite the frequency of m 6 A consensus sites, methylation occurs primarily near stop codons. It will be important to determine how this specificity is achieved and whether cellular mechanisms that involve recognition of the stop codon or the beginning of the 3' UTR are involved in providing specificity to adenosine methylation Stop codon is defined as codon that marks the end of translation. Start and stop codons are important because if start codon is not present then transcript is not translated means protein synthesis is not started as it is the first codon of mRNA translated by ribosome This ability has been achieved previously only in in vivo translational systems, however, with limited functionality. Herein, we report the incorporation of two different unnatural amino acids in response to two different stop codons into one protein, utilizing a cell-free protein synthesis system. Biotechnol Background: Out-of-frame stop codons (OSCs) occur naturally in coding sequences of all organisms, providing a mechanism of early termination of translation in incorrect reading frame so that the metabolic cost associated with frameshift events can be reduced. Given such a functional significance, we expect statistically overrepresented OSCs in coding sequences as a result of a widespread.

Welcome to the Living World: Molecular Basis of

Stop Codon - an overview ScienceDirect Topic

  1. 1 Definition. In der Genetik versteht man unter Stopcodon ein Basentriplett ( Codon) der DNA bzw. RNA, das keine passende tRNA besitzt und so zum Abbruch der Translation und Proteinbiosynthese in einer Zelle führt. Das komplementäre Gegenstück zum Stopcodon ist das Startcodon, das den Beginn einer Translation festlegt
  2. e the fate of the downstream wet lab experiments
  3. Descriptio
  4. 在遗传密码中,终止密码子(英語: Stop codon ),或稱終止子,是信使RNA上的一个核苷酸三联体序列,代表翻译的终止 。 蛋白质是由特定氨基酸生成的多肽序列折叠而成。 轉譯發生時,信使RNA中的大部分密码子被tRNA識別後,tRNA可添加一个额外的氨基酸到成长中的多肽链上,而终止密码子則通过被.
  5. The stop codon usage among the 14 bacterial species is as predicted by the codon-decoder adaptation hypothesis ( fig. 3). First, both LEGs and HEGs follow the same trend with P2 UGA increasing with P RF2 ( P < 0.01 in both LEGs and HEGs, fig. 3). Second, the pattern is stronger in HEGs than in LEGs
  6. remove_stop_codons.py. This script is designed to remove the stop codons TAG, TGA, and TAA in FASTA (.fas) formatted biological data. It takes one FASTA file as input and writes its output to a file called output.fas. Instructions. Place your input file in the directory with remove_stop_codons.py (to keep things organized)
  7. ação (português europeu) ou códon de ter

The codon alignment highlights the occurrence of multiple stop codons (Fig. 2: sites 1 and 2) and the occurrence of frameshifts (Fig. 2: sites 3 and 4.) Stars and exclamation marks in the corresponding AA alignment respectively emphasize these events, which disrupt the coding frame while maintaining the correct translation YES ! You need to remove the stop codons. It can be done by looking on the three frames (+) and choosing the one which is longest. It can be done by ExPASy or by using Unipro Ugene free software.

PPT - Protein Synthesis : DNA Transcription into mRNA and

In this study, we explored the problem of predicting the UAG stop-codon read-through efficiency. The reported nucleotide sequences were first converted into physicochemical property vectors before being presented to a machine learning algorithm. Two sets of physicochemical properties were applied: o A stop codon is a single nucleotide triplet that provides an end-point for protein synthesis. A stop codon tells the ribosome and transfer DNA that the process can stop and the new polypeptide chain can be released. If ribosomes and transfer DNA are still a mystery, either read on or visit the protein synthesis page Stop codon. In the genetic code, a stop codon (or termination codon) is a nucleotide triplet within messenger RNA that signals a termination of translation. Proteins are unique sequences of amino acids, and most codons in messenger RNA correspond to the addition of an amino acid to a growing protein chain — stop codons signal the termination.

A stop codon is a nucleic acid triplet in messenger RNA (mRNA) which does not code for an amino acid, thereby stopping the production of a protein. Stop codons are also present in DNA, so that they carry over when DNA is transcribed into RNA. In DNA, the three stop codons are TAA, TAG, and TGA However, I found more than one stop codon in the middle of the sequences after I translated them to amino acid based on 1 st codon position, 2 nd codon position, and 3 rd codon position. I think.

The three stop codons have been given names - UAG is amber, UGA is opal , and UAA is ochre. Stop codons are also called termination or nonsense codons. They signal the release of the nascent polypeptide from the ribosome because there is no cognate tRNA that has anticodons complementary to these stop signals, and so a release factor binds. Codon stop : définition, explications Le codon stop qualifie le codon qui provoque l'arrêt de la traduction d'une protéine.Il existe trois codons stop : UAA (codon ambre), UAG (codon ocre) et UGA (codon opale). La traduction d'une protéine début avec un codon d'initiation.Les triplets ne codent pour aucun acide aminé mais agissent comme un signal d'arrêt pour la traduction

  1. o acids while the remaining three are used as stop signals. Illustration. Narration. Codon is the name we give a stretch of the three nucleotides, you know, one of A, C, G, or T, three of which in a row, that code for a specific a
  2. ation of the polypeptide chain, so they are also called ter
  3. 氨基酸性质: 非极性: 极性: 碱性: 酸性: 终止密码子:Stop

Stop Codon - The Definitive Guide Biology Dictionar

Le codon stop. Aussi appelé codon de terminaison ou codon non-sens, c'est l'un des trois codons marquant la fin de la traduction d'un ARNm en protéine. En effet, il n'est pas traduit car aucun ARNt ne lui correspond, comme énoncé plus haut. Toutefois, il existe des exceptions. Par exemple, le codon UGA peut éventuellement coder une. use this to remove stop codons from an alignment typically, this would be done to calculate dN/dS in HYPHY Usage: perl./Scripts/ReplaceStopWithGaps.pl -pep 104D5_pep.fasta -nuc 104D5.fasta -output 104D5_nostop.fasta -ref 104D5S1 use this to replace stop codons from the nucleotide alignment with the codon of the reference the nucleotide and the peptide alignments are necessary and the name of. Start and Stop Codons The start codon marks the site at which translation into protein sequence begins, and the stop codon marks the site at which translation ends. Beside above, why is there a stop codon? In the genetic code, a stop codon (or termination codon) is a nucleotide triplet within messenger RNA that signals a termination of. Stop codons affect 5' splice site selection by surveillance of splicing Proc Natl Acad Sci U S A. 2002 Apr 16;99(8):5277-82. doi: 10.1073/pnas.082095299. Authors Binghui Li 1 , Chaim Wachtel, Elana Miriami, Galit Yahalom, Gilgi Friedlander, Gil Sharon, Ruth Sperling, Joseph Sperling. Affiliation 1 Department of.

In the genetic code, a stop codon (or termination codon) is a nucleotide triplet within messenger RNA that signals a termination of translation. Proteins are based on polypeptides, which are unique sequences of amino acids.Most codons in messenger RNA correspond to the addition of an amino acid to a growing polypeptide chain, which may ultimately become a protein Stop codons were historically given many different names, as they each corresponded to a distinct class of mutants that all behaved in a similar manner. These mutants were first isolated within bacteriophages (T4 and lambda), viruses that infect the bacteria Escherichia coli Genetic code. NOTE - starting VarNomen version 3 the '*' is used to indicate a translation stop codon, replacing the 'X' used previously (see Background) These codons act to start or stop protein synthesis. The Protein-sequence algorithm plays only the open reading frame (assume reading frame 1) and non-overlapping codons are mapped to 20 notes, since there are 20 different amino acid residues in a protein. The Tri-nucleotides algorithms plays all codons (64 in total) as individual notes stop codon. Any of the 3 codons (or triplets of nucleotides—UAA, UAG and UGA) on an mRNA molecule which lack a cognate aminoacyl tRNA—i.e., do not code for an amino acid and thus signal the end of protein synthesis. When ribosomes hit a stop codon, mRNA transcription is terminated, causing polypeptide synthesis to stop and the ribosome to.

The stop codon, as its name suggests, is the last translated codon in an mRNA sequence, marking the endpoint for protein synthesis. UAG, UAA, UGA are the three stop codons used in most organisms. ~~~ Stop codon ~~~Title: What is Stop codon? Explain Stop codon, Define Stop codon, Meaning of Stop codonCreated on: 2018-09-08Source Link: https://en.wikipe.. which of the following is not a stop codon. June 8, 2021. 0. 0. ISBN: 9781337392938. B) It never codes for more than one amino acid. It's not fully proven that the same elements will be formed with this substitution and won't be misreading errors. UAG is known as an amber stop codon, UAA is an ochre codon, and UGA is known as an umber stop.

Stop Codon: stop codon definition: The stop codon is the codon that gives end signals to terminate protein synthesis. In 64 combinations of three bases, 61 specify an amino acid, while remaining three combinations are stop codons. These three codons are UUA, UAG, and UGA. These codons also called termination codons or nonsense codons Protein translation begins with a start codon (always AUG → Methionine) and continues until a stop codon (any one of the three: UAA, UAG, or UGA) is reached. mRNA codons are read from 5′ end to 3′ end, and its order specifies the order of amino acids in a protein from N-terminus to C-terminus Therefore, there are 64 possible codon combinations. Sixty-one codons specify amino acids and three (UAA, UAG, UGA) serve as stop signals to designate the end of protein synthesis. The codon AUG codes for the amino acid methionine and serves as a start signal for the beginning of translation. Multiple codons may also specify the same amino acid

The stop codons do not encode for an amino acid. Instead, tell the ribosome that the protein is finished. The three stop codons are U A A, U G A and U A G. The mnemonic here is to think of an annoying person. When an annoying person comes up to you, you're gonna tell them: Stop, U Are Annoying, U Go Away, and U Are Gone. So that's the. Three codons, UAA, UAG, and UGA, are known as stop codons as they stop the process of translation. What is the significance of the triplet code? triplet code. In DNA or mRNA, the sequence of three nucleotides that is the code for a particular amino acid. The triplet sequence controls the amino acid sequence during protein synthesis

START and STOP Codons - Medical New

  1. one stop codon in every 21 codons. Thus, the probability of a random occurrence of even a short open reading frame of say 100 codons without a stop codon is very small (61/ 64)100 = 8.2 x 10-3 Identifying genes in DNA sequences from higher organisms is usally more difficult than in. More ›
  2. Start and stop codons are sites for beginning and ending of translation on mRNA. Start codon is AUG that codes of methionine also. STOP codons are UGA, UAG and UAA. Translation is a major cellular event that translates the information coded in the mRNA in the form of triplet codons to functional protein
  3. o acid. Hence, the process is absolutely specific and focused. Some of the a
  4. ating translation process. A default sequence file is provided in the user interface
  5. o acid. You May Also Enjoy: Difference between Genetic and Physical Mapping. Main Difference between Start Codon and Stop Codon. Start codon base is AUG. Stop codon bases are UAG, UAA, and UGA
  6. a codón de ter

كودون توقف - ويكيبيدي

The stop codon is usually not (I'm tempted to say never) the final sequence before the poly-A-tail. The coding sequence (the RNA region that codes for the protein) occurs in the middle. There is a 5' untranslated region (UTR) before the protein coding region, and a 3' UTR after the protein coding region.. 353 stop codons in the malaria vector, Anopheles gambiae, and of 51 additional Drosophila melanogaster stop codons, including several cases of double and triple readthrough and of readthrough of two adjacent stop codons. We find that most differences between the readthrough repertoires of the two species arose fro Three of these codons are stop codons: UAA, UAG, and UGA. The remaining 61 codons encode 20 amino acids. Out of these 61 codons, the codon AUG (which encodes the amino acid methionine) also serves as a the start signal (start codon) for translation initiation. These codons are similar in all organisms and thus are considered universal

What is the importance of the start and stop codons

Stop kodon atau Kodon stop (Inggris: Stop Codon) atau disebut juga Terminasi kodon atau Penghentian kodon, di dalam molekuler biologi merupakan sebuah Kode genetik atau kodon (nukleotida triplet dalam messenger RNA) yang menandakan penghentian proses translasi pada protein. Kebanyakan kodon dalam messenger RNA berhubungan dengan penambahan asam amino ke rantai polipeptida yang tumbuh, dan. universal genetic code table universal genetic code table. universal genetic code table 28 de janeiro de 2022. difference between individual and group counselling slideshare variables in programming variables in programmin DNA contains 4 bases, A, T, G and C, whereas, proteins are made of 20 different amino acids. Bacteria, fungi, cats, plants, and you: every organism uses DNA to store genetic info

Stop codons are paired with start codons that tell the cellular machinery the beginning of a dna sequence that specifies a specific protein. Methionine is the only amino acid specified by just one codon, aug. Start and stop codons are important because if start codon is not present then transcript is not translated means protein synthesis. If you want to find the first stop codon after a start codon, you can try: Second, it appears that if your regex matches the start codon, it will break the loops and return your list of stop_codons, which assuming every sequence you pass into this function includes a start codon before a stop, would always result in an empty list being returned R Scripts. We implemeted the stop-extended codon model in R and provide the following R scripts to fit and simulate from the model: Given a phylogenetic tree and an in-frame sequence alignment (that includes the stop codon as the last position of the alignment), obtain maximum likelihood estimates of model parameters (stopcodon.rscript).Simulate a codon sequence alignment (including stop codon. The start codon also sets up the reading frame of the DNA strand, indicating that each triplet after that point codes for a specific amino acid. Start and stop codons are found both on the original DNA strand in the nucleus of the cell and on the messenger RNA strand that serves as the protein template 2. ما هو Start Codon 3. ما هو Stop Codon 4. أوجه التشابه بين Start Codon و Stop Codon 5. مقارنة جنبًا إلى جنب - ابدأ Codon مقابل Stop Codon في شكل جدول 6. ملخ

Un codon-stop, codon de terminaison ou encore codon non-sens est l'un des trois codons (parmi les 64 codons du code génétique) qui marquent la fin de la traduction d'un ARNm en protéine.Il n'est en général jamais traduit car il n'existe pas d'ARN de transfert correspondant. Le codon UGA peut cependant, dans les cas exceptionnels des sélénoprotéines, coder une sélénocystéine ; cet. Stop codon A codon is a group of three bases - A, T, C, or G - and codes for a single amino acid, the building blocks of proteins. A stop codon tells the cell's machinery that it has reached the. Stop codon. In the genetic code, a stop codon (or termination codon) is a nucleotide triplet within messenger RNA that signals a termination of translation. [1] Proteins are based on polypeptides, which are unique sequences of amino acids. Most codons in messenger RNA (from DNA) correspond to the addition of an amino acid to a growing. the UAA and UGA stop codons (Korostelev et al, 2008; Laurberg et al, 2008; Weixlbaumer et al, 2008). The structure described here provides an explanation of how RF1 is able to recognize both UAA and UAG stop codons (Figures 2 and 3). As observed for recognition of a UAA codon, three elements of domain 2 of the factor are involved—(1) The N.

Difference Between Codon and Anticodon – Pediaa

Stopcodon - Wikipedi

Stop codon earrings, start codon earrings, engraved gold microbiology earrings, science jewellery, genetics earrings MlNTstudios Sale Price $84.73 $ 84.7 Accordingly, stop codon recognition by eRF1 occasionally can be superseded by a near-cognate aminoacyl-tRNA, resulting in stop codon suppression (also referred to as readthrough). The basal level of termination suppression at naturally occurring stop codons occurs at a frequency of <0.1% ( 84 , 131 ) So recently I've been trying to write a program that detects and cuts out the coding part of a DNA sequence based on start and stop codons. The eventual goal is to compare 2 sequences of both 240 nucleotides long, however one causes sickle-cell disease, so you want to see the difference between the coding parts that both result Stop Codons Are Not Reassigned in Peritrichs. A recent study profiling stop codon usage in 33 ciliates across nine classes revealed that all 33 show stop codon reassignment (Pan et al., 2019). Most (30 out of 33) of the species investigated use either TAA or TGA as the biased stop codon and reassign the other two stop codons to code amino acids This is because in random sequence, a codon has 3/64 chance of being a stop codon, so in a frame-shifted gene sequence there suddenly are many. The premature stop codon will prematurely end the first round of translation, but if any machinery for the splicing of the mRNA is still present (it is not at the normal stop codon), the mRNA will be.


Start and Stop Codons - YouTub

Stop codons are responsible for releasing new polypeptide chains formed from the ribosomes. They do not code for an amino acid. You May Also Enjoy: Difference between Genetic and Physical Mapping. Main Difference between Start Codon and Stop Codon. Start codon base is AUG. Stop codon bases are UAG, UAA, and UGA While Loops 9:30. While Loop Syntax and Semantics 3:06. Coding While Loops 6:45. Three Stop Codons 5:03. Coding Three Stop Codons - Part I 7:45. Coding Three Stop Codons - Part II 4:35. Logical And / Or 8:01. Coding And / Or 6:52. Finding Multiple Genes 5:16 a. a codon that specifies the same amino acid as the original codon b. a stop codon c. an amino acid substitution that alters the tertiary structure of the protein d. an amino acid substitution at the active site of an enzym

What is a Stop Codon? - Biology Wis

Stop codon much preferred by E coli is TAA than the environment TAG. Different proteases or translation is post deformed phage. All proteins affect phage following translation stop codon is translational codon to develop drugs that translation systems that is involved in. The stop codons; its roles for downstream of post stop codons are. DNA sequences corresponding to the stop codons, the results are presented as TAA, TAG, and TGA sequences. The distri-bution of stop codons within and across phyla varies dramati-cally (Fig. 1). Although in Actinobacteria, TGA is the predom-FIGURE 1. Stop codon distribution in different bacterial phyla How many codons code for stop codons? 3. This hypothesis states that the first two nucleotides in a codon are more critical than the third. Wobble Hypothesis. Based on this, mutations in the _____ nucleotide typically have less affect on the amino acid coded for and therefore, the protein structure Translation of stop codon in French. Typically, SepRS preferentially aminoacylates tRNASep with O-phosphoserine and the tRNASep recognizes at least one codon such as a stop codon. Typiquement, SepRS aminoacyle de préférence ARNtSep avec de la O-phosphosérine et l'ARNtSep reconnaît au moins un codon tel qu'un codon non-sens

Genetic code - Wikipedi

Start Codon: It is a universal codon and the very first nucleotide of messenger RNA that initiates any process of gene formation. AUG ( Adenine, Uracil, and Guanine) codes for Methionine which is a start codon. Stop Codon: Codons are 64 in totality but only 61 codes for an amino acid. The three remaining do not code for anything hence the term. Three Stop Codons 5:03. Coding Three Stop Codons - Part I 7:45. Coding Three Stop Codons - Part II 4:35. Logical And / Or 8:01. Coding And / Or 6:52. Finding Multiple Genes 5:16. Translating to Code 8:00. Taught By. Owen Astrachan. Professor of the Practice. Robert Duvall. Lecturer . Andrew D. Hilton use this to replace stop codons from the nucleotide alignment: the nucleotide and the peptide alignments are necessary : Raw ReplaceStopWithGaps.pl This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters

Comprehensive Analysis of mRNA Methylation Reveals

frame stop codons upstream of the latent site in intron N (Fig. 1a Lower), gave similar results (Fig. 1b, CAD2). Notably, neither constructs gave rise to latent splicing. However, eliminating all stop codons from both of them allowed latent splicing in the respective mutants, as predicted by the model and detailed below Python Tripos. Logistic growth model: Consider the discrete logistic model. x [n+1] = r * x [n] * (1 - x [n]) modeling the growth of a single population, where x [n] is the density of the population at n-th generation and r is the growth rate. Fix the growth rate r = 3.1 and initial population density x [0] = 0.43 There is 1 codon for start. It is AUG, which is the amino acid Methionine. There are 3 stop codons. They are UAA, UAG, and UGA. A 3 base code could specify a maximum of 64 amino acids, so 64-4. Assertion :- t RNAs are specific for each amino acid but there are no t-RNAs for stop codons. Reason : The secondary structure of t-RNA has been depicted that looks like a colver-leaf. A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion. B

Is ATC a stop codon? - AskingLot

exclusively into the TAA, TAG, and TGA STOP codons (Figures 1B, 1C, and S1D). CAA, CAG, and CGA triplets can be con-verted into STOP codons when modified by CRISPR-depen-dent base editors on the coding strand, while TGG can be converted into STOP codons if targeted on the non-coding strand (Figures 1C, S1A, and S1B) Codons. Cells decode mRNAs by reading their nucleotides in groups of three, called codons. Here are some features of codons: Most codons specify an amino acid. Three stop codons mark the end of a protein. One start codon, AUG, marks the beginning of a protein and also encodes the amino acid methionine An open reading frame is a portion of a DNA molecule that, when translated into amino acids, contains no stop codons. The genetic code reads DNA sequences in groups of three base pairs, which means that a double-stranded DNA molecule can read in any of six possible reading frames--three in the forward direction and three in the reverse The presence of amber stop codons within the antibody sequence causes the premature termination of soluble form of scFv expression in nonsuppressor Escherichia coli strain. In the present study, we have used a novel strategy that allows soluble expression of scFvs having amber stop codon in their gene sequences (without phage PIII protein. Nonsense mutations turn a coding (sense) codon into an in-frame stop codon that is assumed to result in a truncated protein product. Thus, nonsense substitutions are the hallmark of pseudogenes and are used to identify them. Here we show that in-frame stop codons within bacterial protein-coding genes are widespread. Their evolutionary conservation suggests that many of them are not pseudogenes.