Cloning and characterization of the CYS3 (CYI1) gene of Saccharomyces cerevisiae

B. I. Ono, K. Tanaka, K. Naito, C. Heike, S. Shinoda, S. Yamamoto, S. Ohmori, T. Oshima, E. A. Toh

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A DNA fragment containing the Saccharomyces cerevisiae CYS3 (CYI1) gene was cloned. The clone had a single open reading frame of 1,182 bp (394 amino acid residues). By comparison of the deduced amino acid sequence with the N- terminal amino acid sequence of cystathionine γ-lyase, CYS3 (CYI1) was concluded to be the structural gene for this enzyme. In addition, the deduced sequence showed homology with the following enzymes: rat cystathionine γ- lyase (41%), Escherichia coli cystathionine γ-synthase (36%), and cystathionine β-lyase (25%). The N-terminal half of it was homologous (39%) with the N-terminal half of S. cerevisiae O-acetylserine and O- acetylhomoserine sulfhydrylase. The cloned CYS3 (CYI1) gene marginally complemented the E. coli metB mutation (cystathionine γ-synthase deficiency) and conferred cystathionine γ-synthase activity as well as cystathionine γ- lyase activity to E. coli; cystathionine γ-synthase activity was detected when O-succinylhomoserine but not O-acetylhomoserine was used as substrate. We therefore conclude that S. cerevisiae cystathionine γ-lyase and E. coli cystathionine γ-synthase are homologous in both structure and in vitro function and propose that their different in vivo functions are due to the unavailability of O-succinyl-homoserine in S. cerevisiae and the scarceness of cystathionine in E. coli.

Original languageEnglish
Pages (from-to)3339-3347
Number of pages9
JournalJournal of bacteriology
Issue number10
Publication statusPublished - 1992

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


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