Ulf Lagerkvist

STRUCTURE AND FUNCTION OF TRANSFER RNA. I. SPECIES SPECIFICITY OF TRANSFER RNA FROM E. COLI AND YEAST.

The valyl, phenylalanyl and leucyl RNA synthetases have been partially purified from yeast. The species specificity of these enzymes and the corresponding enzymes from Escherichia coli has been studied with regard to yield and reaction rate. All of the yeast enzymes could esterify transfer RNA from E. coli while, of the E. coli enzymes, only valyl RNA synthetase could esterify yeast RNA. The leucyl RNA synthetase from yeast only recognized about 60% of the sites available on E. coli RNA. The reaction rates were in every case considerably lower with heterologous RNA than with homologous RNA. The chromatographic behaviour of amino acyl RNAs synthesized with homologous and non-homologous enzymes has been studied on methylated albumin columns.

Readinbg of the lysine codons in the MS 2 coat protein cistron during protein synthesis in vitro

The translation of the genetic information contained in the messenger RNA is based on the recognition between codon and anticodon. The first two positians of the codon are read by the anticodon strictly according to the rules of classic base pairing. Wowever, in the reading of the third codon position by the wobble nucleotide of the a~tic~dQ~ a greater degree of freedom must be postulated in order to allow for the discrepancy between the large number of codons in a degenerate code and the limited number of anticodons available for reading them. In his wobble hypothesis [I] Crick has laid down the restrictions which presumably govern the reading of the third codon position. Obviously, the reading of this position must be restricted in alI cases where there would otherwise be a mistake in the synthesized protein. For intance, in the phenyl~~ine~eu~~e codon group QJUU, UUC, UUA and UUG), an anticodon with Gin the wobble position cannot recognize the codons UUA and UUG because that would lead to the in~oduction of phenyl~an~e instead of leucine. We have introduced the term codon family to denote a group of four codons which all code for the same amino acid and we have asked ourselves if the rules of the wobble hypothesis apply as strictly here