Properties of isoaccepting tRNA-Val from rabbit reticulocytes; fractionation and codon recognition

Aminoacyl-transfer RNA populations in mammalian cells chromatographic profiles and patterns of codon recognition

The chromatographic profiles of 20 aminoacyl-tRNAs from rabbit liver were compared to those of rabbit reticulocytes by reverse phase chromatography and the chromatographic profiles of 20-aminoacyl-tRNAs from bovine liver were compared to those of bovine brain. The two rabbit tissues showed significant differences in the elution profiles of most aminoacyl-tRNAs, while the elution profiles of the aminoacyl-tRNAs from the bovine tissues showed fewer differences. The patterns of codon recognition of several aminoacyl-tRNAs fractionated from rabbit reticulocytes have also been compared to those fractionated from rabbit liver.

Rabbit liver tRNA1Val:I. Primary structure and unusual codon recognition

The major valine acceptor tRNA1Val from rabbit liver was purified and its nucleotide sequence determined by in vitro [32P] - labeling with T4 phage induced polynucleotide kinase and finger-printing techniques. Its primary structure was found to be identical with the major valine tRNA from mouse myeloma cells. According to the wobble hypothesis this tRNA, which exclusively has an IAC anticodon, should decode the valine codons GUU, GUC and GUA only. However, this tRNA recognizes all four valine codons with a surprising preference for GUG. It is unknown whether this is due to the lack of A37 modification next to the 3' end of the anticodon IAC. The nature of the inosine-guanosine interaction remains to be clarified.

The primary structure of rabbit beta-globin mRNA as determined from cloned DNA

The rabbit beta-globin DNA insertion of the hybrid plasmid PbetaG1 (Maniatis et al., 1976) was sequenced by the method of Maxam and Gilbert (1977). A sequence of 576 nucleotides was determined and verified by pyrimidine tract analysis of double-stranded DNA, synthesized in vitro starting from beta-globin mRNA. The derived sequence is in complete agreement with previously reported partial mRNA sequencing data and with the predictions from the primary structure of the protein. Moreover, the globin DNA insertion is missing only 13 nucleotides corresponding to the 5' terminal sequence of the mRNA. The rabbit beta-globin mRNA consists of a coding region of 438 nucleotides, flanked by a 5' noncoding region of 56 nucleotides (including the initiation codon AUG but not the 7-methyl-guanine of the "cap structure") and by a 3' noncoding region of 95 nucleotides (including a UGA termination codon). The features of the mRNA sequence are discussed with specific attention to the selective use of particular codons, the probable existence extensively base-paired segments at the 5' terminal region and the ribosome binding site. The faithful representation of beta-globin mRNA in the PbetaG1 DNA insertion establishes the validity of used cloned DNA, initially derived from double-stranded DNA transcripts of mRNA, for studying the structure of eucaryotic genes.