Cell Cycle-Regulated Transcription of the CLB2 Gene Is Dependent on Mcm1 and a Ternary Complex Factor

Abstract

Clb2 is the major B-type mitotic cyclin required for entry into mitosis in the budding yeast Saccharomyces cerevisiae. We showed that accumulation of CLB2 transcripts in G2 cells is controlled at the transcriptional level and identified a 55-bp upstream activating sequence (UAS) containing an Mcm1 binding site as being necessary and sufficient for cell cycle regulation. Sequences within the cell cycle-regulated UAS were shown to bind Mcm1 in vitro, and mutation which abolished Mcm1-dependent DNA binding activity eliminated cell cycle-regulated transcription in vivo. A second protein with no autonomous DNA binding activity was also recruited into Mcm1-UAS complexes, generating a ternary complex. A point mutation in the CLB2 UAS which blocked ternary complex formation, but still allowed Mcm1 to bind, resulted in loss of cell cycle regulation in vivo, suggesting that the ternary complex factor is also important in control of CLB2 transcription. We discuss the possibility that the CLB2 gene is coregulated with other genes known to be regulated with the same periodicity and suggest that Mcm1 and the ternary complex factor may coordinately regulate several other G2-regulated transcripts.

Mechanisms controlling differential promoter-occupancy by the yeast forkhead proteins Fkh1p and Fkh2p: implications for regulating the cell cycle and differentiation

“…Because Fkh1p and Fkh2p can have measurably different effects on the transcription of CLB2 in vivo, and because both proteins can bind this promoter in vivo (Koranda et al 2000;Kumar et al 2000), the relative occupancy of the CLB2 promoter by Fkh1p and Fkh2p is crucial for proper CLB2 expression. In addition, Fkh2p, but not Fkh1p, is a component of SFF (Swi five factor) (Koranda et al 2000;Kumar et al 2000;Pic et al 2000;Zhu et al 2000), a partially characterized protein complex that binds to promoters of genes in the CLB2 cluster at sites required for their cell cycle-regulated transcription (Lydall et al 1991;Althoefer et al 1995;Maher et al 1995). Consistent with this observation, Fkh2p occupies CLB2-cluster promoters in vivo more efficiently than Fkh1p (Koranda et al 2000;Kumar et al 2000).…”

“…Our in vitro analysis revealed two biochemical differences between Fkh1p and Fkh2p. First, purified Fkh2p, but not Fkh1p, could bind cooperatively with itself, and second, Fkh2p, but not Fkh1p, could bind cooperatively with Mcm1p, a second gene regulatory protein required for transcription of genes in the CLB2 cluster (Lydall et al 1991;Althoefer et al 1995;Maher et al 1995). The latter difference provided an explanation for the differences in relative promoter-occupancy by Fkh1p and Fkh2p at a variety of promoters in vivo.…”

“…4). Mcm1p is required for DNA binding by SFF to CLB2-cluster promoters and proper expression of genes within the CLB2 cluster (Lydall et al 1991;Althoefer et al 1995;Maher et al 1995;Kumar et al 2000). The SUN4 and SPS4 genes were identified as potential non-CLB2-cluster gene targets of Fkh1p/Fkh2p by genome expression analysis of a fkh1⌬ fkh2⌬ strain (Zhu et al 2000); neither gene contains a predicted match to a Mcm1p-binding site.…”

A novel Mcm1-dependent element in the SWI4, CLN3, CDC6, and CDC47 promoters activates M/G1-specific transcription.

“…Mcml is also required for transcription of the G2-specific transcripts (Lydall et al 1991;Althoefer et al 1995;Maher et al 1995), which are transcribed immediately before the wave of ECB-activated transcription (see Fig. 6).…”

Fkh2p and Sep1p regulate mitotic gene transcription in fission yeast

“…These elements are responsible for G2/M-specific expression through the mitotic cell cycle (Althoefer et al, 1995;Maher et al, 1995;Koranda et al, 2000;Kumar et al, 2000;Pic et al, 2000). Mcm1p recruits the forkhead transcription factor Fkh2p and this complex remains bound to promoters throughout the cell cycle (Althoefer et al, 1995;Hollenhorst et al, 2000;Koranda et al, 2000;Kumar et al, 2000;Pic et al, 2000;Zhu et al, 2000).…”