THE NUCLEOTIDE-SEQUENCE OF SACCHAROMYCES-CEREVISIAE CHROMOSOME-IV

The complete DNA sequence of the yeast Saccharomyces cerevisiae chromo some IV has been determined. Apart from chromosome XII, which contains the 1-2 Mb rDNA cluster, chromosome IV is the longest S. cerevisiae c hromosome. It was split into three parts, which were sequenced by a co nsortium from the European Community, the Sanger Centre, and groups fr om St Louis and Stanford in the United States. The sequence of 1,531,9 74 base pairs contains 796 predicted or known genes, 318 (39.9%) of wh ich have been previously identified. Of the 478 new genes, 225 (28.3%) are homologous to previously identified genes and 253 (32%) have unkn own functions or correspond to spurious open reading frames (ORFs). On average there is one gene approximately every two kilobases. Superimp osed on alternating regional variations in G+C composition, there is a large central domain with a lower G+C content that contains all the y east transposon (Ty) elements and most of the tRNA genes. Chromosome I V shares with chromosomes II, V, XII, XIII and XV some long clustered duplications which partly explain its origin.