Cell Size and Cln-Cdc28 Complexes Mediate Entry into Meiosis by Modulating Cell Growth

Abstract

In the yeast Saccharomyces cerevisiae, mitotic cell cycle progression depends upon the G1-phase cyclin-dependent kinase Cln-Cdc28 and cell growth to a minimum cell size. In contrast,Cln-Cdc28 inhibits entry into meiosis, and a cell growth requirement for sporulation has not beenestablished. Here, we report that entry in meiosis is also dependent upon cell growth. Moreover,sporulation and cell growth rates were proportional to cell size; large cells grew rapidly andsporulated sooner while smaller cells grew slowly and sporulated later. In addition, Cln2 proteinlevels were higher in smaller cells suggesting that Cln-Cdc28 activity represses meiosis insmaller cells by preventing cell growth. In support of this hypothesis, loss of Clns, or thepresence of a cdc28 mutation increased cell growth in smaller cells and accelerated meiosis inthese cells. Finally, over-expression of CLNs repressed meiosis in smaller cells, but not in largecells. Taken together, these results demonstrate that Cln-Cdc28 represses entry into meiosis inpart by inhibiting cell growth.