Genomic Exploration of the Hemiascomycetous Yeasts: 10.Kluyveromyces thermotolerans

Abstract

A genomic exploration of Kluyveromyces thermotolerans was performed by random sequence tag (RST) analysis. We sequenced 2653 RSTs corresponding to inserts sequenced from both ends. We performed a systematic comparison with a complete set of proteins from Saccharomyces cerevisiae, other completely sequenced genomes and SwissProt. We identified six mitochondrial genes and 1358^1496 nuclear genes by comparison with S. cerevisiae. In addition, 25 genes were identified by comparison with other organisms. This corresponds to about 24% of the estimated gene content of this organism. A lower level of conservation is observed with orthologues to genes of S. cerevisiae previously classified as orphans. Gene order was found to be conserved between S. cerevisiae and K. thermotolerans in 56.5% of studied cases. ß

Genomic Exploration of the Hemiascomycetous Yeasts: 13. Pichia angusta

“…Yet, a sequence of 20 nucleotides around the transcription initiation site for the 35S rRNA and two short segments of 20 and 15 nucleotides located, respectively, 281 and 230 bases downstream of this site, are identical in the two species. Given the number of RSTs sequences identi¢ed to encode rRNA and the estimated size of P. angusta genome, the total number of rDNA repeats is only 25, which is very much less than what is observed in S. cerevisiae [15] or Kluyveromyces thermotolerans [16] but is similar to values obtained for the other species of this project.…”

Genomic Exploration of the Hemiascomycetous Yeasts: 20. Evolution of gene redundancy compared to Saccharomyces cerevisiae

“…2 that homologues to S. cerevisiae singletons are systematically slightly less numerous than expected. This phenomenon is attributable to the presence of a number of questionable ORFs in the predicted set of singletons (see [14]). …”

Genomic Exploration of the Hemiascomycetous Yeasts: 9. Saccharomyces kluyveri

“…We also found the homologue of dihydroorotate dehydrogenase (PYRD) from Arabidopsis thaliana, another gene involved in pyrimidine catabolism, probably in the ¢rst step of pyrimidine degradation (Piskur, personal communication). Homologues of these genes were also identi¢ed in K. thermotolerans [28], Y. lipolytica [30], K. lactis [31] and P. angusta [32], but not in the other Saccharomyces species. The presence/absence of this pathway is consistent with the phylogenetic separation of the species.…”

“…S. kluyveri is the only Saccharomyces species which is D-glucitol positive [26]. Homologues of the SOU1 gene were also identi¢ed in K. marxianus [27] and K. thermotolerans [28], the closest species to S. kluyveri, which are also D-glucitol positive [29]. Homologues of three genes encoding enzymes for the conversion of 5-substituted hydantoins to corresponding L-amino acids were identi¢ed (AMAB, ylbB, and HYUc).…”