CLN1 and Its Repression by Xbp1 Are Important for Efficient Sporulation in Budding Yeast

Abstract

Xbp1, a transcriptional repressor of Saccharomyces cerevisiae with homology to Swi4 and Mbp1, is induced by stress and starvation during the mitotic cycle. It is also induced late in the meiotic cycle. Using RNA differential display, we find that genes encoding three cyclins (CLN1, CLN3, andCLB2), CYS3, and SMF2 are downregulated when Xbp1 is overexpressed and that Xbp1 can bind to sequences in their promoters. During meiosis, XBP1 is highly induced and its mRNA appears at the same time asDIT1 mRNA, but its expression remains high for up to 24 h. As such, it represents a new class of meiosis-specific genes. Xbp1-deficient cells are capable of forming viable gametes, although ascus formation is delayed by several hours. Furthermore, Xbp1 target genes are normally repressed late in meiosis, and loss of XBP1 results in their derepression. Interestingly, we find that a deletion of CLN1 also reduces the efficiency of sporulation and delays the meiotic program but that sporulation in a Δcln1 Δxbp1 strain is not further delayed. Thus, CLN1 may be Xbp1's primary target in meiotic cells. We hypothesize that CLN1 plays a role early in the meiotic program but must be repressed, by Xbp1, at later stages to promote efficient sporulation.

ACKNOWLEDGMENTS

We thank Nancy Kleckner, Harvard University, for providing the SK-1 strains and Ron Reeder, Fred Hutchinson Cancer Research Center, for the pFA-kanMX6 plasmid. Special thanks are offered to Ingrid Wolf, Christoph Sachsenmaier, and other members of the laboratory for numerous constructive suggestions and discussions.

This work was supported by NIH grant GM41073 to L.B. and by a Deutsche Forschungsgemeinschaft postdoctoral fellowship to B.M.