Coordinated regulation of gene expression by the cell cycle transcription factor Swi4 and the protein kinase C MAP kinase pathway for yeast cell integrity.

Abstract

Specific transcription in late G1, mediated by the transcription factors SBF (Swi4p-Swi6p) and MBF (Mbplp-Swi6p), is crucial for cell cycle progression in budding yeast. In order to better understand the G1/S transition, we initiated a search for conditional mutations synthetic lethal with swi4A. One of the isolated mutants, rsf8swi4A, showed a growth defect due to cell lysis. rsf8 is allelic to PKCJ, encoding a protein kinase C homologue which controls cell integrity. In the presence of the rsf8/(pkcl-8) mutation, a functional SBF but not MBF is required for viability. Importantly, swi4A and swi6A strains are hypersensitive to calcofluor white and SDS, indicating that they possess a weakened cell wall. Overexpression or ectopic expression of CLN did not suppress the pkc1-8swi4A mutant phenotype, thus SBF must control cell integrity independently, rather than acting through CLN expression. We found that at least six genes involved in cell wall biosynthesis are periodically expressed at the G1/S phase boundary. In all six cases, cell cycleregulated expression is due mainly to Swi4p. Finally, we found that the PKCI MAP kinase pathway is a positive regulator of five of these cell wall genes, these genes being novel targets of regulation by this pathway. We suggest that SBF and the PKCJ MAP kinase pathway act in concert to maintain cell integrity during bud formation.

Comprehensive Identification of Cell Cycle–regulated Genes of the YeastSaccharomyces cerevisiaeby Microarray Hybridization

“…We can ask whether genes below the threshold might still be cell cycle regulated in a biologically significant way, and we can consider whether there are any circumstances in which our experiments might have failed to reveal the cell cycle pattern of regulation. In this context it is relevant that we do not identify 9 of the 104 genes (CDC8,DBF4,CHS3,PRI1,TIR1,CDC14,CLB3,DPB3,and RAD17) previously reported to be cell cycle regulated (White et al, 1987;Chapman and Johnston, 1989;Siede et al, 1989;Johnston et al, 1990b;Fitch et al, 1992;Wan et al, 1992;Igual et al, 1996;Caro et al, 1998). Of these, only RAD17 appears visually to vary with the cell cycle in our data and then only in the cdc15 experiment.…”

Prenylation of Saccharomyces cerevisiae Chs4p Affects Chitin Synthase III Activity and Chitin Chain Length

“…The obvious answer would seem to be that, under normal circumstances, Chs3p is not saturated with Chs4p and that cellular levels of Chs4p represent one of the factors that regulate the availability of active enzyme. Other factors that may produce increased chitin synthesis include moderately increased transcription of CHS4 and CHS3 (6,18,20,40) and alterations in the localization of the enzyme (8,15,42). However, this attractive hypothesis needs to be proven.…”

The effect of tea tree oil and antifungal agents on a reporter for yeast cell integrity signalling

“…The fact that membrane-destabilizing drugs such as SDS and chlorpromazine affect yeast cell integrity (Igual et al, 1996;Kamada et al, 1995) suggested that TTO may also affect signalling. For this investigation, the effective TTO concentrations in the genetic background of S. cerevisiae strain HD56-5A needed to be determined.…”