Multiplicity of serine-specific transfer RNAs of brewer's and baker's yeast

Abstract

The major and minor tRNA Ser species were isolated from brewer's and baker's yeast and characterized by various analytical procedures. Their behavior in a number of chromatographic and countercurrent distribution systems is discussed. Some properties of tRNA Ser aggregates are described. The rates of aminoacylation of the various tRNA Ser species have been compared. The multiplicity of tRNA Ser is related to the following facts: (1) The occurrence of different tRNA Ser species for the various serine codons. The major species tRNA Ser 1 and tRNA Ser 2 have the anticodon IGA and respond to U-C-U, U-C-C, and U-C-A. The minor species tRNA Ser 3a and tRNA Ser 3b, which respond to A-G-C (and A-G-U), have been characterized now. tRNA Ser species for U-C-G are either absent or present in rather small amounts (tRNA Ser x?). (2) The previously described, and functionally still unexplained, differences in three nucleotides between tRNA Ser 1 and tRNA Ser 2 of brewer's yeast. (3) Multiple peaks are also created by the presence of N 4- acetylcytidine or cytidine, respectively, in position 12 of the chains of tRNA Ser 1 and tRNA Ser 2. The degree of acetylation depends on the nutritional state of the yeast. Both the major tRNA Ser species and the A-G-C-responding minor species tRNA Ser 3a and tRNA Ser 3b were also found after cloning and sporulation of the yeast. Methods of deacetylating the N 4- acetylcytidine residue and determining the N 4- acetylcytidine content of tRNAs have been developed. With that, appropriate substrates and methods are available now permitting the search for a specific acetyl-incorporating enzyme.