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During the cell division cycle of the yeast Saccharomyces cerevisiae,
the G1-to-S transition depends upon the activation of two
transcription factors (SBF and MBF), which are responsible for
the cell cycle-regulated expression of more than 200 genes. Bck2
becomes essential in the absence of Cln3, the most upstream
activator of this transcriptional program. Here we have used a
genome-wide approach to elucidate the targets of Bck2. Our data
indicate that Bck2 activates a selection of cell cycle-regulated genes
from all cell cycle stages. In contrast, Cln3 activates only G1/S phase
genes. Furthermore, Bck2 activates many genes independently of
Swi6, the common component of SBF and MBF. Comparison of
Bck2 targets with those of other transcription factors suggests that,
in addition to SBF and MBF, Bck2 may elicit gene expression via
Ste12 and Mcm1. We propose that Bck2 activates its targets by a
mechanism fundamentally different from that of Cln3, and that it
may be a necessary cofactor for the full expression of a subset of cell
cycle-regulated genes.
Thanks to Sylvia Gutiérrez Erlandsson for technical assistance with flow cytometry, Herman Wijnen for providing plasmid pML1 (pRS313-MET3pCLN2), Victor Parro and his lab for sharing the GenePix scanner, and people of the CYC group for their helpful discussions. This work was funded by the Ministerio de Ciencia e Innovación of Spain (Consolider-Ingenio 2010), and the European Union (FEDER). F.F. is a researcher of the Ramón y Cajal program. |
