Isolation and characterization of an invertase and its repressor genes from Schizosaccharomyces pombe

PCR was used to isolate an invertase homolog gene from the fission yeast Schizosaccharomyces pombe. The cloned inv1⁺ gene encodes a protein of 581 amino acids with 16 potential asparagine-linked glycosylation sites, and has 39% and 38% identity to the Schwanniomyces occidentalis and Saccharomyces cerevisiae SUC2 invertases. When the inv1⁺ gene was disrupted, S. pombe strains lacked detectable invertase activity. This result showed that the inv1⁺ gene encodes only one active invertase in S. pombe cells. The transcription of inv1⁺ is repressed in the presence of glucose. The transcription of inv1⁺ was not affected in cyr1Δ strain which lacks adenylate cyclase activity, unlike transcription of S. pombe fbp1⁺ gene. We have identified an S. pombe gene (scr1⁺) that encodes a homolog of the Aspergillus nidulans CREA which is required for glucose repression of the glyconeogenic pathway. Although the deletion of scr1⁺ did not influence the transcription of fbp1⁺ gene, glucose repression of the inv1⁺ gene was severely affected. These results showed that glucose repression of inv1⁺ gene is dependent on scr1⁺ gene, and S. pombe cAMP signalling pathway may not be essential for glucose repression of inv1⁺ gene.