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Biomedical subjects

U Lagerkvist

Publications and source records attributed to U Lagerkvist.

At least 19 recordsLinked to original sources
PubMed1989

Codon discrimination and anticodon structural context.

Site-directed mutagenesis has been used to change the nucleotide C in the wobble position of tRNA(1Gly) (CCC) to U. The mutated tRNA was tested for its ability to read glycine codons in an in vitro protein-synthesizing system programmed with the phage message MS2-RNA that had been modified by site-directed mutagenesis so as to make it possible to monitor conveniently the reading of all four glycine codons. The results showed that while the efficiency of tRNA(1Gly) (UCC) was comparable to that of mycoplasma tRNA(Gly) (UCC) in the reading of the codon GGA, the mycoplasma tRNA(Gly) was far more efficient than the tRNA(1Gly) (UCC) in the reading of the codons GGU and GGC. Thus, the anticodon UCC, when present in the structural context of the tRNA(1Gly) molecule, behaved as predicted by the wobble rules while in the structural context of the mycoplasma tRNA(Gly) it read without discrimination between the nucleotides in the third codon position, in violation of the wobble restrictions. The result with the codon GGG showed that the anticodon UCC, when present in tRNA(1Gly), was considerably less efficient in reading this codon than it was in the structural context of the mycoplasma tRNA(Gly). It would therefore seem that the anticodon UCC, when present in a certain tRNA, can be an efficient wobbler, while in the molecular environment of another tRNA it is markedly restricted in its ability to wobble.

Amino Acid Sequence↗
PubMed1987

Apparent lack of discrimination in the reading of certain codons in Mycoplasma mycoides.

We report a cluster of four tRNA genes from Mycoplasma mycoides as well as the sequence of the alanine, proline, and valine tRNAs and the serine tRNA reading the UCN codons (where N stands for G, A, C, or U). This brings the total number of tRNA genes that we have so far characterized in this organism to 14, 6 of which code for tRNAs that read the codons of family boxes. In each of these latter cases, we found only one gene per family box, and the gene sequence contains a thymidine in the position corresponding to the wobble nucleotide, with the exception of the arginine tRNA gene that has an adenosine in this position. Furthermore, all of the tRNA structures reported here have an unsubstituted uridine in the wobble position. These findings are similar to those reported for mitochondria, especially yeast mitochondria, that contain an arginine tRNA with the anticodon ACG. However, the resemblance is not complete since we have demonstrated the presence of two isoacceptor tRNAs for threonine having uridine and adenosine, respectively, in the wobble position. It is suggested that in the M. mycoides at least some of the family codon boxes are read by only one tRNA each, using an unconventional method without discrimination between the nucleotides in the third codon position.

Base Sequence↗
PubMed1979

Relative efficiency of anticodons in reading the valine codons during protein synthesis in vitro.

Using a protein synthesizing in vitro system programmed with MS 2-RNA, the relative efficiency (in the presence of each other) of valine tRNAs with the anticodons U*AC (U* represents 5-oxyacetic acid uridine monophosphate), GAC, and IAC to read the valine codons was investigated. An anticodon which can read all three positions of the codon according to the rules of Watson-Crick base-pairing and the wobble hypothesis is an order of magnitude more efficient than an anticodon which misreads the codon by reading only the first two positions and presumably disregards the third nucleotide of the codon. There are two seeming exceptions to this behavior: the anticodon U*AC reads the codon GUU quite efficiently and IAC is as effective as U*AC in reading the codon GUG. The significance of these exceptions is evaluated with respect to the organization and evolution of the genetic code.

Anticodon↗
PubMed1978

"Two out of three": an alternative method for codon reading.

An alternative method for codon reading, whereby only the first two codon nucleotides are recognized by the anticodon, is discussed and the experimental evidence for this "two of three" reading method is reviewed. Misreading of codons by the "two out of three" method could pose a significant threat to the fidelity of protein synthesis unless the genetic code is organized in such a way as to prevent this method from being used when it might compromise translational fidelity. Inspection of the genetic code shows that it is arranged in such a way that the "two out of three" reading method can be used without translational errors.

Anticodon↗
PubMed1977

Aminoacyl adenylate, a normal intermediate or a dead end in aminoacylation of transfer ribonucleic acid.

The shape of the time curve for the aminoacylation of tRNA has been investigated using five different amino acid:tRNA ligases. Four of these enzymes showed a lag in the time curve during the early phase of the first catalytic turnover of the enzyme. In each case, the lag period could be abolished by preincubating the ligase with amino acid, ATP, and Mg2+ under conditions known to give an aminoacyl adenylate-enzyme complex. With all five ligases the steady state rate of transfer from the preformed aminoacyl-adenylate complex to tRNA was approximately the same as that of the overall reaction.

Adenosine Monophosphate↗
PubMed1977

Codon-acticodon recognition in the valine codon family.

An in vitro protein-synthesizing system completely dependent on added valine tRNA (valyl-tRNAval) and programmed with RNA from the phage MS2 has been used to investigate the incorporation into MS2 coat protein of valine from isoaccepting valyl-tRNAsval with the anticodons U AC (U represents 5-oxyacetic acid uridine monophosphate), GAC, and IAC in response to the four valine codons GUU, GUC, GUA, and GUG. By examining the incorporation of valine into NH2-terminal and internal positions of three tryptic peptides from the MS2 coat protein it has been established that these anticodons each recognize all four valine codons. We therefore conclude that under our conditions of in vitro protein synthesis the genetic code, as far as the valine codons are concerned, is operationally a two letter code, i.e. the third codon nucleotide has no absolute discriminating function.

Amino Acid Sequence↗