Disease relevance of tRNA-Trp

• The only observed difference in specificity between the E. coli and yeast systems was for tRNATrp, which was aminoacylated on the 2'-position in E. coli and the 3'-position in yeast [1].
• The ability of tryptophan tRNA (tRNATrp) to initiate reverse transcription of the 70S RNA of avian RNA tumor viruses suggested that the reverse transcriptase (RNA-dependent DNA polymerase; deoxynucleosidetriphosphate: DNA deoxynucleotidyltransferase; EC 2.7.7.7) might have a specific binding site for the tRNA [2].

High impact information on tRNA-Trp

• A gene for Saccharomyces cerevisiae tRNATrp has been sequenced which contains an intervening sequence of 34 bp (H. S. Kang and J. Abelson, unpublished results) [3].
• A nuclear extract from Xenopus oocytes is capable of supporting transcription of the tRNATrp gene contained on plasmid pBR313 [3].
• DNA sequence analysis of this gene revealed that the mitochondrial tRNATrp anticodon is 5'UCA3'. Because there is a U in the wobble position, this tRNA can recognize and insert tryptophan into a growing polypeptide chain in response to the nonsense codon UGA [4].
• This RNA was transcribed from a cluster of repetitive sequences: both intact and truncated delta and sigma elements adjacent to a tRNATrp gene [5].
• Transcripts from this hybrid gene were found to be processed by endonuclease and ligase at the tRNATrp exon-intron boundaries [6].

Biological context of tRNA-Trp

• The rate of aminoacylation of the procaryotic tRNATrp by the enzyme is three orders of magnitude lower [7].
• The sequence of wheat germ tRNATrp as determined by [32P] post-labelling techniques is: [sequence in text] The interesting features are: (i) Presence of a C11:G24 base pair in contrast to the U11:G24 in E. coli Su- tRNATrp [8].
• Oxidized tRNATrp (but not tRNATrp without the 3'-A) accelerates tryptophan-dependent hydrolysis of ATP catalyzed by the enzyme [9].
• The pattern of phosphate alkylation of tRNATrp is very similar to that found with other tRNAs studied before using the same approach with protected phosphates mainly located in the D and T psi arms [10].
• The Saccharomyces cerevisiae haploid genome includes six copies of the gene encoding tRNATrp which are scattered on five chromosomes [11].

Anatomical context of tRNA-Trp

• The anticodon of bean mitochondria tRNATrp is CmCA, which can recognize UGG (the codon for tryptophan in the universal code) and is complementary neither to UGA (which codes for tryptophan in mammalian and yeast mitochondria) nor to CGG (which could be a tryptophan codeword in plant mitochondria) [12].
• The Michaelis constants and the maximum velocities in the aminoacylation reaction of tRNATrp from beef liver, yeast and E. coli by pure beef pancreas tryptophan-tRNA ligase show that this mammalian enzyme recognizes and charges the two eucaryotic tRNAs with the same efficiency [7].

Associations of tRNA-Trp with chemical compounds

• Once tRNATrp is added to the synthetase.adenylate complex, the protective effect of the adenylate disappears [9].
• The same effects are found also in the presence of tRNATrp oxidized with NaI04 and tRNATrp lacking the 3'-terminal adenosine [9].
• Alkylation in beef tRNATrp of phosphodiester bonds by ethylnitrosourea and of N-7 in guanosines and N-3 in cytidines by dimethyl sulfate and carbethoxylation of N-7 in adenosines by diethyl pyrocarbonate were investigated under various conditions [10].
• The method has been applied for mapping exposed cytosine bases in tRNATrp (yeast) which have been found in the anti-codon loop and at the 3'-end of the molecule [13].
• Analysis of the base compositions showed that isoacceptor B differed from isoacceptor A in one respect only: 2'-O-methylguanosine, a modified guanosine base occurring at position 17 of the major isoacceptor A tRNATrp, was not detectable in hydrolysates of purified isoacceptor B [14].

Analytical, diagnostic and therapeutic context of tRNA-Trp

• We have used site-directed mutagenesis to convert the anticodon of a cloned tRNATrp gene from CCA to CTA with the expectation that this gene would produce tRNA molecules capable of interacting with the UAG terminator codon [15].
• Northern blot analyses of the steady state levels of tRNATrp in cells containing the high copy-number clones reveal 20-100% increases in the abundance of tRNATrp [16].

References