NUCLEOTIDE-SEQUENCE OF THE SCHIZOSACCHAROMYCES-JAPONICUS VAR VERSATILIS RIBOSOMAL-RNA GENE-CLUSTER AND ITS PHYLOGENETIC IMPLICATIONS

Fission yeasts form a small but heterogeneous group of ascomycetes and it is still unclear whether they should be subdivided into three gene ra (Schizosaccharomyces, Octosporomyces, Hasegawaea) or remain a singl e genus (Schizosaccharomyces). In order to decide whether a new genus Hasegawaea should be established for the species Schizosaccharomyces j aponicus and Schizosaccharomyces versatilis, we have characterized the entire rDNA cluster in Schizosaccharomyces japonicus var. versatilis and compared it with the homologous region from Schizosaccharomyces po mbe and with complete rRNA gene sequences from other yeast genera. Fro m a phage genomic library a recombinant lambda phage containing the en tire rDNA repeat unit was isolated. In this paper we report the primar y sequence of the Iss, 5.8s and 25s rRNA coding regions. The S. japoni cus var. versatilis rRNA genes are 1823 (18s), 158(5.8s) and 3422 (25s ) nucleotides long. The two sequences of the larger rRNA genes exhibit 95.7% (18s)and 93% (25s) similarity with the homologous genes from S, pombe. The differences between the rRNA genes of S. japonicus and S. pombe, however, are much smaller than the intrageneric differences wit hin the rDNA sequences of other yeast genera. Therefore, subdivision o f fission yeasts into the genera Schizosaccharomyces and Hasegawaea do es not to seem to be justified. The sequence has been deposited in the EMBL data bank under the accession number Z 32848.