PRIMARY STRUCTURE OF ISOLEUCINE TRANSFER RIBONUCLEIC ACID FROM TORULOPSIS UTILIS - COMPLETE DIGESTION WITH RIBONUCLEASES AND CONSTRUCTION OF MODEL OF ITS SECONDARY STRUCTURE

Isoleucine tRNA from Torulopsis utilis was purified by column chromatography on DEAE-Sephadex. The tRNA was obtained in a purity of about 95%, which is probably one of the purest preparation of tRNA specific for a single amino acid. All of the fragments from the complete digests with pancreatic RNase [EC 2.7.7. 16] and RNase T1 [EG 2. 7. 7. 26] were isolated and analyzed mainly by column chromatography. The analyses indicated that this tRNA is composed of 77 nucleotide residues. Thirteen unusual nucleotides are present, including N-(purin-6-ylcarbamoyl)-threonine ribonucleo-tide. It is the first time that this nucleotide has been isolated from a pure specific tRNA.A model of the unique secondary structure of this tRNA can be constructed from the fragments formed by the two RNases, according to known general features of a clover leaf type of arrangement. © 1969 BY THE JOURNAL OF BIOCHEMISTRY.