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Over-expression of S. cerevisiae G1 cyclins restores the viability of alg1 N-glycosylation mutants

Benton, B.K., Plump, S.D., Roos, J., Lennarz, W.J., Cross, F.R.
Current genetics 1996 v.29 no.2 pp. 106-113
Saccharomyces cerevisiae, mutants, alleles, proteins, cell division, chemical reactions, glycosyltransferases, structural genes, nucleotide sequences, amino acid sequences, gene expression, messenger RNA, mutation, transcription (genetics)
In budding yeast, one of three G1 cyclins is required for progression though START, when cells commit to a further round of cell division. We have identified mutations in ALG1 (ERC14), a gene required for N-glycosylation, which are inviable in a cln1 cln2 background but are rescued by over-expression of CLNs. CLN1 and CLN2 are much more efficient than CLN3 in rescuing the erc14-1 allele. The erc14-1 allele results in a significant N-glycosylation defect, and no rescue of this defect by CLN1 over-expression was detected. These data suggest that CLN over-expression could be allowing cells to live with lower levels of N-glycosylation, possibly by overcoming a checkpoint sensitive to N-glycosylation capacity. A plasmid suppressor of alg1, PSA1, encodes a 361 amino-acid protein with homology to NDP-hexose pyrophosphorylases, the enzymes that catalyze the formation of activated sugar nucleotides. PSA1 is an essential gene, and PSA1 transcription is nearly co-ordinately regulated with CLN2 transcription, peaking near START. Co-ordinate regulation of glycosylation, sugar nucleotide metabolism, and cell-cycle progression through G1 may be a feature that ensures adequate cell-wall precursors are present before bud emergence.