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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Influence of rare codons upon gene expression in E. coli was investigated. The chimeric gene was created combining CAT gene and a fragment of the gene, encoding for alpha-domain of beta-galactosidase. The synthetic oligonucleotides were inserted in different parts of the chimeric gene. The constructed synthetic oligonucleotides encoded the same amino acid sequences and contained arginine codons AGG, AGA and CGT in various combinations. It was shown that the presence of rare arginine codons AGG and AGA in the template and their mutual arrangement significantly influence the level of gene expression. At the same time the presence of leucine, isoleucine, glycine and proline rare codons does not cause such an effect. Translation of AGGAGG and AGAAGA sequences was found to lead to the formation of a considerable amount of polypeptides of incomplete length. It was shown that the presence of such a cluster of rare codons effects on the length of specific mRNA.
Mol Biol (Mosk)
PMID:[Rare codons and gene expression in Escherichia coli]. 147 Jan 73

Influence of increased arginine concentrations of tRNA's corresponding to rare codons AGG and AGA was studied in the model system constructed earlier. The model system is a chimeric gene consisting of CAT gene fragment, part of the gene encoding for alpha-domain of beta-galactosidase E. coli and a series of synthetic inserts enriched with codons AGG and AGA. In order to increase the intracellular tRNA concentration the natural gene of AGA-specific tRNA and the artificial gene of AGG-specific tRNA were cloned in plasmid under the control of p15A ori compatible with co1EI ori and used for maintaining the model gene. It was shown that the artificial AGG-specific tRNA gene produces a functionally active tRNA. A steep rise in the synthesis of polypeptide encoded by the model template containing rare codons was demonstrated when the genes of tRNAs recognizing these codons were propagated in the multicopy plasmid. It was shown that AGA-specific tRNA efficiently translates both AGA and AGG codons while AGG-specific tRNA - only AGG codons.
Mol Biol (Mosk)
PMID:[The effect of intracellular concentrations of tRNA, corresponding to the rare arginine codons AGG and AGA, on the gene expression in Escherichia coli]. 147 Jan 74

The inherent infidelity of Taq DNA polymerase in the polymerase chain reaction was exploited to produce random mutations in the trp A gene. Screening of the resulting clones allowed selection of non-interactive mutant alpha subunits retaining their intrinsic catalytic activity. Two single changes responsible for this phenotype were identified by DNA sequencing as: alpha 126 valine (GTG)----glutamic acid (GAG) and alpha 128 valine (GTT)----aspartic acid (GAT). Three single changes giving a non-interactive phenotype with an impaired intrinsic catalytic activity were identified by DNA sequencing as alpha 66 asparagine (AAC)----aspartic acid (GAC); alpha 109 lysine (AAA)----arginine (AGA); alpha 118 cysteine (TGC)----arginine (CGC). Where possible, we individually assessed the importance of these residues in alpha beta interaction in light of structural information from X-ray crystallography and by intergeneric protein sequence comparison.
Mol Gen Genet 1992 May
PMID:Selection and analysis of non-interactive mutants in the Escherichia coli tryptophan synthase alpha subunit. 160 55

We have recently identified a tRNA gene cluster in the Arabidopsis nuclear genome. One tRNA(Ser) (AGA) gene and two tRNA(Tyr) (GTA) genes occur in tandem arrangement on a 1.5 kb unit that is amplified about 20-fold at a single chromosomal site. Here we have studied the in vitro expression of seven individually cloned tRNA(Ser) genes (pAtS1 to pAtS7) derived from this cluster. Five out of the seven tRNA(Ser) genes contain point mutations in the coding region which have in part adverse effects on the expression of these genes in different cell-free systems: (i) C10 and A62 in plant tRNA(Ser) genes, which correspond to G10 and C62, respectively, in all known vertebrate tRNA genes, result in a reduced transcription efficiency in HeLa but not in yeast extract. This indicates that yeast RNA polymerase III tolerates nucleotide substitutions at positions 10 [5' internal control region (ICR)] and 62 (3' ICR), whereas the vertebrate RNA polymerase III requires a more stringent consensus sequence. (ii) Processing of a pre-tRNA(Ser) with a mismatch in the aminoacyl stem is impaired in HeLa, yeast and wheat germ extracts, however, a mismatch in the anticodon stem is deleterious for HeLa and wheat germ but not for yeast processing enzymes. The unexpectedly high number of potential tRNA(Ser) pseudogenes in the cluster - quite in contrast to the tRNA(Ser) genes which mainly code for functional tRNAs - suggested that tRNA(Ser) (AGA) genes also occur elsewhere in the genome. We present evidence that single copies of tRNA(Ser) (AGA) genes do indeed exist outside the tRNA gene cluster.
Mol Gen Genet 1992 May
PMID:Expression of variant nuclear Arabidopsis tRNA(Ser) genes and pre-tRNA maturation differ in HeLa, yeast and wheat germ extracts. 160 62

The suspect human hepatocarcinogen aflatoxin B1 (AFB1) is a well-known potent initiator of hepatic tumors in rainbow trout (Oncorhynchus mykiss). Both hepatocellular carcinomas and mixed hepatocellular/cholangiocellular carcinomas are induced by AFB1 in trout, with the mixed form predominating. We previously isolated two c-ras genes from trout liver cDNA, and in the present study we analyzed DNA from 14 AFB1-induced trout liver tumors for point mutations in exon 1 of both genes. Using the polymerase chain reaction (PCR) and oligonucleotide hybridization methods, a high proportion (10/14) of the AFB1-initiated tumor DNAs showed evidence of activating point mutations in the trout c-Ki-ras gene. Of the 10 mutant ras genotypes, seven were codon 12 GGA----GTA transversions, two were codon 13 GGT----GTT transversions, and one was codon 12 GGA----AGA transition. Nucleotide sequence analysis of cloned PCR products from four of these tumor DNAs provided definitive evidence for two codon 12 GGA----GTA mutations, one codon 12 GGA----AGA mutation, and one codon 13 GGT----GTT mutation, in complete agreement with the oligonucleotide hybridization results. No mutations were detected in exon 1 of a second trout ras gene also expressed in liver, nor in DNA from control livers. This is the first report of experimentally induced ras gene point mutations in a lower vertebrate fish model. The results indicate that the hepatocarcinogen AFB1 induces c-Ki-ras gene mutations in trout similar to those in rat liver tumors.
Mol Carcinog 1991
PMID:Analysis of ras gene mutations in rainbow trout liver tumors initiated by aflatoxin B1. 164 72

Hepatitis B surface antigen (HBsAg) particles carry the common determinant, a, as well as d or y and w or r subtype determinants, and are classified into the four major subtypes, i.e., adw, adr, ayw and ayr. Rare sera contain HBsAg particles with all four subtype determinants (adywr). Target sequences (nucleotides 38-550) in the S gene of hepatitis B virus (HBV) DNA in two such sera were amplified by the polymerase chain reaction. Individual amplification products were cloned in an M13 phage vector. The HBV DNA clones obtained were subtyped by determining the second letters of codon 122 and 160 for lysine (AAA/AAG) or arginine (AGA/AGG), which specify the d or y and w or r determinants, respectively. From one serum (S-63), two adw, 10 adr and 58 ayr clones were obtained. When the two adw clones and two representatives each of the adr and ayr clones were compared against each other, for the sequence of 235 base pairs representing nucleotides 295-529 in the S gene, they differed only by 0.4-2.1% (average 1.2%). These results indicated multiple point mutations of a single HBV strain of subtype ayr and co-infection of hepatocytes with the original HBV strain and its mutant of subtype adw as the mechanism for the production of HBsAg/adywr particles. From the other serum (K-45), 1 adw, 73 adr and 4 ayw clones were obtained. The adw clone and two representative adr clones differed only by 0-1.7% in the S gene sequences, but they differed by 8.5% or greater from two representative ayw clones. HBsAg/adywr particles in this serum, therefore, could be explained by double infection of hepatocytes with two HBV strains of different subtypes (adr and ayw).
Mol Immunol 1990 May
PMID:Hepatitis B surface antigen particles with all four subtypic determinants: point mutations of hepatitis B virus DNA inducing phenotypic changes or double infection with viruses of different subtypes. 169 59

The localization of meprobamate-like (MPB-like) molecules in the neuromuscular junction of rats has been investigated at light- and electron- microscopic levels with the peroxidase-antiperoxidase (PAP) immunohistochemical method, using a purified antiserum obtained from rabbits immunized with a meprobamate-bovine serum albumin (MPB-BSA) conjugate. The immunoreaction was found surrounding synaptic vesicles and in protuberant deposits situated in the post-synaptic membrane. These facts suggest the existence of endogenous MPB-like molecules in neuromuscular junction and that the immunostained protuberant deposits should mark the receptors of those molecules.
Cell Mol Biol 1991
PMID:Presence of meprobamate-like molecules in rat neuromuscular junction. Immunohistochemical demonstration at light- and electron-microscopic levels. 187 23

The supF gene of the shuttle vector pZ189 was used as a target for the study of mutations induced by cis-diamminedichloroplatinum(II) (cis-DDP). Normal human repair-proficient fibroblasts and cis-DDP repair-deficient xeroderma pigmentosum (XP) cells were used as host cells to study the effect of cis-DDP on the inhibition of shuttle vector replication and mutagenesis. Transfection of cis-DDP-treated pZ189 into normal and XP cell lines resulted in a marked increase in the mutation frequency and a decrease in the replication efficiency of the vector. However, these effects were much greater for the plasmid propagated in XP cells. Atomic absorption spectroscopy showed that six to eight Pt-DNA adducts per plasmid were necessary to inhibit plasmid replication by 50% in normal cells. In contrast, only one to two Pt-DNA adducts were necessary to inhibit replication of the plasmid by 50% in XP cells. Analysis of mutation sites demonstrated that cis-DDP treatment resulted primarily in single and double mutations separated by one base and limited to a few locations within the 85-bp mature tRNA. Propagation of the cis-DDP-treated vector in either normal or XP cells led to predominantly transversion mutations at AGA, AGG, and GAG sites and a cis-DDP-associated deletion of 174 bp. Although mutations occurred at target sites for cis-DDP adduct formation, there was no correlation between sites of mutation and the most frequent sites of adduct formation.
Mol Carcinog 1991
PMID:Spectrum of cis-diamminedichloroplatinum(II)-induced mutations in a shuttle vector propagated in human cells. 191 Apr 83

We argue that in animal mitochondria codon reassignments, such as those for AGA and AGG from arginine to serine or of AUA from isoleucine to methionine, are the result of an interplay between biased mutational forces and selective ones. In particular, there is a marked tendency for animal mitochondria to have very small genomes and to minimize their investment in components required for gene expression. These tendencies are expressed as a reduction in the diversity of tRNA isoacceptor species. In our view, the pressure to simplify tRNA populations, together with mutational bias against certain codons, will account for the codon reassignments observed in animal mitochondria. A parallel to the major codon bias in microorganisms, which likewise tends to reduce the diversity of the tRNA isoacceptor populations under fast growth conditions, may be drawn. Therefore, we suggest that codon reassignments are usefully viewed as an extreme form of codon bias.
Mol Biol Evol 1991 Jul
PMID:An extreme codon preference strategy: codon reassignment. 192 8

AGA and AGG (AGR) are arginine codons in the universal genetic code. These codons are read as serine or are used as stop codons in metazoan mitochondria. The arginine residues coded by AGR in yeast or Trypanosoma are coded by arginine CGN throughout metazoan mitochondria. AGR serine sites in metazoan mitochondria are occupied mainly in corresponding sites in yeast or Trypanosoma mitochondria by UCN serine, AGY serine, or codons for amino acids other than serine or arginine. Based on these observations, we propose the following evolutionary events. AGR codons became unassigned because of deletion of tRNA Arg (UCU) and elimination of AGR codons by conversion to CGN arginine codons. Upon acquisition by serine tRNA of pairing ability with AGR codons, some codons for amino acids other than arginine mutated to AGR, and were captured by anticodon GCU in serine tRNA. During vertebrate mitochondrial evolution, AGR stop codons presumably were created from UAG stop by deletion of the first nucleotide U and by use of R as the third nucleotide that had existed next to the ancestral UAG stop.
J Mol Evol 1989 Sep
PMID:Evolution of the mitochondrial genetic code. I. Origin of AGR serine and stop codons in metazoan mitochondria. 250 56


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