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Results for “Codon, Initiator”

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PubMed1988

Biosynthesis of reovirus-specified polypeptides: effect of point mutation of the sequences flanking the 5'-proximal AUG initiator codons of the reovirus S1 and S4 genes on the efficiency of mRNA translation.

The effect on translation of site-directed nucleotide substitutions around the 5'-proximal AUG initiation codon of the reovirus s1 mRNA specifying polypeptide sigma 1 and the reovirus s4 mRNA specifying polypeptide sigma 3 was examined. The efficiency of synthesis of the S1-encoded sigma 1 polypeptide and the S4-encoded sigma 3 polypeptide was analyzed in transfected simian COS cells. Mutant s1 mRNAs possessing either GCU AUG G or GCA AUG G sequences surrounding the 5'-proximal sigma 1 AUG were translated with an efficiency comparable to that of the wild-type s1 mRNA which possesses the flanking sequence CCU AUG G. Mutant s4 mRNAs possessing either CCU AUG G or CCA AUG G sequences surrounding the 5'-proximal sigma 3 AUG were translated with an efficiency comparable to that of wild-type s4 mRNA which possesses the flanking sequence GCA AUG G. The s4 mRNAs, both wild-type and mutant, were translated in vivo about five times more efficiently than the s1 mRNAs, both wild-type and mutant. These results suggest that nucleotide positions other than the -3, -2, -1, and +4 positions relative to the 5'-proximal initiator AUG, where the A is +1, play a dominant role in determining the efficiency of translation of these two reovirus mRNAs in vivo.

Codon↗

PubMed1994

Initiation codons within 5'-leaders of mRNAs as regulators of translation.

Why should a preponderance of proto-oncogenes, growth factor genes and growth factor receptor genes contain translation initiation codons and associated open reading frames in their 5'-leaders? An increasing number of open reading frames are being shown to function as cis-acting regulatory signals able to moderate expression of the downstream reading frame. These regulatory elements could play a fundamental role in the regulation of proliferation of vertebrate cells.

Codon↗

PubMed1981

Nucleotide sequence coding for the respiratory NADH dehydrogenase of Escherichia coli. UUG initiation codon.

The nucleotide sequence of the structural gene coding for the respiratory NADH dehydrogenase of Escherichia coli has been determined by the chain-termination method. The reading frame for the protein starts with the unusual initiation codon UUG and predicts an amino acid sequence of 434 residues (Mr = 47 304). The reading frame was confirmed by protein chemical studies including determination of the N-terminal sequence of the protein. The product made in vivo was found to have threonine as its N-terminal residue, indicating that the initiating N-formylmethionine had been removed by post-translational processing.

Amino Acid Sequence↗

PubMed1988

[Location of the initiating codon AUG in relation to the 5'-end of mRNA mediates the effectiveness of translation in E. coli cells].

A semisynthetic gene for beta-galactosidase (lacZ) and a synthetic DNA fragment containing the "ideal" promoter sequence were used for construction of an artificial operon including translation initiation codon ATG and no SD sequence. Cloning this artificial operon into pBR322 vector resulted in a number of pV plasmids; ATG positions were varied by insertions of synthetic oligonucleotides between lacZ coding sequence and starting point of transcription. It was found that efficiency of beta-galactosidase synthesis in E. coli cells harbouring pV plasmids strongly depended on the relative position of AUG and mRNA 5'-end. High level of the synthesis was provided by translation of mRNA with AUG codon in 5'-terminal position. Amounts of synthesized beta-galactosidase diminished with increase of the distance (2, 4, and 5 nucleotides) between 5'-end of lacZ mRNA and AUG codon.

Base Sequence↗

PubMed2003

Mitochondrial localization of antizyme is determined by context-dependent alternative utilization of two AUG initiation codons.

Ornithine decarboxylase-antizyme (Az), a polyamine-induced protein that targets ornithine decarboxylase (ODC) to rapid degradation, is synthesized as two isoforms. Studies performed in vitro indicated that the 29 and 24.5 kDa isoforms originate from translation initiation at two alternative initiation codons. Using transient transfections we demonstrate here that also in cells the two isoforms are synthesized from two AUG codons with the second being utilized more efficiently. The more efficient utilization of the second AUG is due to its location within a better sequence context for translation initiation. By using immunostaining we demonstrate that only the less expressed long form of Az is localized in the mitochondria. Moreover, this long isoform of Az and not the more efficiently expressed short isoform is imported into mitochondria in an in vitro uptake assay. Our data therefore demonstrate that a single Az transcript gives rise to two Az proteins with different N-terminal sequence and that the longer Az form containing a potential N-terminal mitochondrial localization signal is transported to mitochondria.

Journal Article↗

PubMed1990

[New single point mutation at the initiation codon (ATG-AGG) identified in amplified genomic DNA of a Chinese with beta-thalassaemia].

A new single nucleotide change at nt 2 of exon 1 of the beta-globin gene was identified in a Chinese female patient with beta-thalassaemia. Dot blot hybridization of the amplified genomic DNA with oligonucleotide probes showed that she carried the four base deletions at the codons 41/42. Direct DNA sequencing on the amplified DNA revealed that she also carried a new mutation (ATG-AGG) at the initiation codon on the other beta-globin gene. This single nucleotide change abolishes a NcoI recognition site and hence it can be directly visualized after gel electrophoresis. Analyses of restriction fragment length polymorphisms showed that she also carried a rightward -3.7 kb (type I) deletion in her alpha-globin genes, and is in fact a alpha beta-thalassaemia genotype.

Base Sequence↗

PubMed1986

Effects of GUG and AUG initiation codons on the expression of lacZ in Escherichia coli.

We have replaced the ribosomal binding site (RBS) of the lacZ gene of E. coli by those of the maturation (A) gene of phage MS2 and that of the tufA gene. Both RBSs contain a GUG initiation codon. The expression with the tufA RBS is at least 25-fold higher than with the phage RBS. Changing the GUG into AUG results in a 3-fold increase in expression in both cases. In general, higher expression is accompanied by an increase of lac-specific mRNA. It is argued that this is a consequence of the more efficient translation of the mRNA.

Base Sequence↗

PubMed1997

Context sequences of translation initiation codon in plants.

In this survey of 5074 plant genes for their AUG context sequences, purines are present at the -3 and +4 positions in about 80% of the sequences. Although this observation is similar to the vertebrate consensus sequence, the number of plant mRNAs with purines at the -3 position is lower and at the +4 position is higher than reported for vertebrate mRNAs. Higher plants have an AC-rich consensus sequence. caA(A/C)aAUGGCg as a context of translation initiator codon. Between the two major groups of angiosperms, the context of the AUG codon in dicot mRNAs is aaA(A/C)aAUGGCu which is similar to the higher-plant consensus but monocot mRNAs have c(a/c)(A/G)(A/C)cAUGGCG as a consensus which exhibits an overall similarity with the vertebrate consensus. The experimental evidence regarding the importance of the AUG context in plants is discussed.

Codon↗

PubMed1982

Systematic alteration of the nucleotide sequence preceding the translation initiation codon and the effects on bacterial expression of the cloned SV40 small-t antigen gene.

In the preceding paper (Derom et al., 1981) we described the cloning in bacterial plasmids of the simian virus 40 (SV40) small-t antigen gene under transcriptional control of the bacteriophage lambda pL promoter. Systematic variation of the distance and/or nucleotide sequence between the Shine-Dalgarno ribosome interaction sequence and the small-t translation initiation codon leads to considerable differences in production of small-t by the different plasmids. Secondary structure models derived for the different mRNAs confirm our previous conclusions about the requirement first for an accessible start codon and second for an accessible ribosome interaction site for efficient translation initiation. Secondary structure models for mRNAs from plasmids containing the small-t gene under control of the lac promoter are in agreement with these conclusions.

Antigens, Viral↗

PubMed1994

Rps3 and rpl16 genes do not overlap in Oenothera mitochondria: GTG as a potential translation initiation codon in plant mitochondria?

Characterization of the Oenothera mitochondrial ribosomal gene cluster rps19-rps3-rpl16 shows the two genes rps3 and rpl16 to be separated by 9 nucleotides. The first codon of rpl16 is a GTG codon for valine and the only potential translational start. This GTG codon is conserved at the same position in maize, Petunia and Marchantia mitochondria, while sequences diverge upstream. These observations suggest that GTG at least at this position may act as translation initiation codon in plant mitochondria. Analysis of RNA editing suggests both genes to code for functional ribosomal proteins in Oenothera mitochondria. A duplication/recombination event at a decanucleotide in the intron of rps3 created a pseudogene missing part of the intron and the 3' exon.

Amino Acid Sequence↗

PubMed1990

Drosophila choline acetyltransferase uses a non-AUG initiation codon and full length RNA is inefficiently translated.

RNA from a partial cDNA clone containing the entire protein coding sequence of Drosophila melanogaster acetyl-CoA:choline O-acetyltransferase (EC 2.3.1.6; choline acetyltransferase) can be translated into active enzyme. This is unusual since this partial cDNA clone contains no appropriate ATG (AUG) initiation codon. In this study we use in vitro deletion and point mutants to identify GTG as the starting codon for protein translation. We also report the sequence of a full length Drosophila choline acetyltransferase cDNA and demonstrate that RNA produced by this clone is translated into active choline acetyltransferase but at a significantly reduced efficiency when compared to the partial cDNA clone. These results indicate that translational control may be an important regulatory step in production of Drosophila choline acetyltransferase.

Amino Acid Sequence↗

PubMed1993

Initiation codon mutations in the Chlamydomonas chloroplast petD gene result in temperature-sensitive photosynthetic growth.

The chloroplast petD gene encodes subunit IV of the cytochrome b6/f complex and is required for photosynthetic electron transport. We have created Chlamydomonas strains in which the initiation codon of the petD gene has been changed to AUU or AUC. These mutants can grow photosynthetically at room temperature, but not at 35 degrees C. The accumulation of subunit IV during photosynthetic or heterotrophic growth at room temperature is reduced to 10-20% of the wild-type level; petD mRNA abundance is reduced to approximately 50% of the wild-type amount. Pulse labeling experiments indicate that at room temperature, subunit IV translation proceeds at 10-20% of the wild-type rate. Cells grown heterotrophically at 35 degrees C accumulate < 5% as much subunit IV as wild-type cells grown under the same conditions, and < 1% as much subunit IV as wild-type cells grown at room temperature. We conclude that translation initiation in these mutants is inefficient, leading to decreased translation and accumulation of subunit IV. At 35 degrees C, translational inefficiency leads directly or indirectly to insufficient accumulation of subunit IV to support photosynthetic growth.

Animals↗

PubMed1991

mRNA leader length and initiation codon context determine alternative AUG selection for the yeast gene MOD5.

MOD5, a nuclear gene of Saccharomyces cerevisiae, encodes two isozymic forms of a tRNA-modification enzyme. These enzymes modify both cytoplasmic and mitochondrial tRNAs. Two inframe ATGs of the MOD5 gene are used for initiation of translation, and the form of the protein translated from the first AUG is imported into mitochondria. Protein translated from the second AUG functions in the cytoplasm. Since all transcripts contain both of these translational start sites and two proteins are made, the question arises as to the factors that influence the translation start-site choice. Extending the 5' ends of the MOD5 mRNA to include leader sequences of the ADH1 (alcohol dehydrogenase defective) transcript produces significant changes in the choice of AUGs. This suggests that for wild-type MOD5 transcripts, the length or structure of the leader sequence plays a role in AUG choice. The nucleotides surrounding the first ATG of MOD5 also have an effect on translation initiation. Altering these nucleotides changes initiation choice and suggests that ribosomal bypass of a suboptimal AUG is another mechanism controlling the alternate use of two initiation codons. Our data support the model that at least one MOD5 transcript is able to produce two proteins with different N-terminal sequences.

Alkyl and Aryl Transferases↗

PubMed1991

Identification of the initiation codon of plum pox potyvirus genomic RNA.

The expression of plum pox potyvirus (PPV) genomic RNA takes place through translation of its unique long and functional open reading frame (ORF) into a large polyprotein that undergoes extensive proteolytic processing. In this paper we show that the AUG recognized as the initiation codon of the PPV ORF by in vitro translation systems is the one found at nucleotide position 147, in spite of the presence at position 36 of an in-phase AUG that marks the start of the ORF. Deletion of a substantial part of the PPV 5' nontranslated region (5'-NTR), from nucleotide 19 to 101, does not impair the in vitro translation of PPV synthetic transcripts. By introduction of mutations that disrupt either of these two AUGs into a full-length PPV cDNA clone, it is shown that, while alteration of the first AUG does not have any effect on virus viability, growth, or symptom induction, destruction of the second renders the viral RNA noninfectious. This result indicates that the AUG employed in vivo is also the second. The hypothesis that this AUG could be recognized through a ribosomal internal entry mechanism has been tested in vitro using various bicistronic transcripts in which the PPV 5'-NTR was internally placed. The second cistron of these bicistronic RNAs was translated, but only at low levels, indicating that the PPV 5'-NTR is not able to drive in vitro an efficient internal entry of the ribosomes and suggesting that PPV RNA translation might proceed through a conventional leaky scanning mechanism.

Base Sequence↗

PubMed1985

[Localization of initiating codons in RNA prokaryotes messengers by learning technics].

Learning processes are applied to the recognition of protein coding regions in prokaryotes. Non-contradictory, statistical rules are deduced from a set of known examples of coding regions. These rules allow us to build characteristic patterns on the m-RNA upstream the initiating codon. These rules are applied to recognize more than 180 coding sequences.

Cell Physiological Phenomena↗

PubMed1990

Human peroxisomal L-alanine: glyoxylate aminotransferase. Evolutionary loss of a mitochondrial targeting signal by point mutation of the initiation codon.

The amino acid sequence of human hepatic peroxisomal L-alanine: glyoxylate aminotransferase 1 (AGTI) deduced from cDNA shows 78% sequence identity with that of rat mitochondrial AGTI, but lacks the N-terminal 22 amino acids (the putative mitochondrial targeting signal). In humans this signal appears to have been deleted during evolution by a point mutation of the initiation codon ATG to ATA. These data suggest that the targeting defect in primary hyperoxaluria type 1, in which AGT1 is diverted from the peroxisomes to the mitochondria, could be due to a point mutation that reintroduces all or part of the mitochondrial signal sequence.

Alanine Transaminase↗

PubMed1987

An alpha-globin gene initiation codon mutation in a black family with HbH disease.

The molecular basis of hemoglobin H disease in a Black family of Canadian origin was investigated. Affected individuals had a combination of deletion and nondeletion alpha-thalassemia mutations on different chromosomes. Cloning and sequencing of the DNA of one member with the nondeletion form revealed a new thalassemia mutation, an A----G substitution, in the initiation codon of the remaining alpha-globin gene of a rightward (-alpha 3.7) deletion chromosome. This mutation abolished an Ncol restriction site and therefore is detectable in genomic DNA by Southern blot analysis.

Black People↗

PubMed1979

Deletion mutants of polyoma virus defining a nonessential region between the origin of replication and the initiation codon for early proteins.

Mutants of polyoma virus with deletions as large as 90 base pairs were isolated by selecting spontaneously arising genomes resistant to endonuclease HaeII or by treating HaeII- or BglI- cleaved linear DNAs with S1 nuclease and exonuclease III. All of the mutants were viable and, therefore, defined a nonessential region in the polyoma genome between the origin of DNA replication and the initiation codon for translation of early proteins. Several mutants with large deletions had altered growth properties, giving smaller plaques and lower virus yields than the parental wild-type virus. These viruses may lack sites that are important for DNA replication or for transcription and translation of early mRNA's. All of the mutants tested could transform BHK-21 cells to anchorage independence.

Animals↗