Cell Cycle Regulated Gene Expression in Yeasts - Advances in Genetics - page 74

It is likely that other protein kinases are involved in controlling cell
cycle transcription factors as many are phosphoproteins, and these need to be
identified. And of course, the fact that transcription factors are reversibly
phosphorylated means that the antagonistic phosophatases require identification
as well.

C. Evolution of cell cycle control mechanisms
An interesting question is how cell cycle transcriptional control mechanisms
have evolved. Now that we have models in different organisms, comparative
studies can permit this to be approached. Global analyses have already made
interesting inroads into this area, suggesting how relatively simple mutations can
have profound implications for expression of groups of genes, and so can account
for major differences in circuitry between species (de Lichtenberg et al. , 2007;

Jensen et al. , 2006; Tuch et al. , 2008a,b).

D. Meiosis
Though this review has deliberately focused on mitotic control, it is important to
state that some of the mechanisms described also operate during the alternative
life cycle, meiosis. In a few cases, related or the same transcription factor
complexes operate, with forkhead transcription factors and MBF being good
examples (Abe and Shimoda, 2000; Cunliffe

,. 1998;
Raithatha and Stuart, 2005). But in many other cases, completely different
transcription factors and promoter sequences specific to meiotic gene expression
are present, although the same simple paradigm operates with various waves of
gene expression being controlled by specific transcription factors and promoter
sequences (Chu

et al. , 2004; Horie et al

et al. , 1998; Mata et al. , 2002).

E. Mediator complex
There has been much interest in characterizing the Mediator complex in both
budding and fission yeasts, with the complex now well described and its pattern
of binding to DNA in a global context characterized (Holstege

et al ., 1998;

Linder , 2006). As well as its more general role in forming

the link between RNA polymerase II and the specific transcription factors that
control regulated gene expression, it has been found that the Mediator complex
has a more specific role in controlling cell cycle gene expression in both yeasts.
For example, mutations in components of the Mediator complex in fission yeast
have specific effects on the transcription of genes required late in the cell cycle
for cell separation under Ace2p and possibly Sep1p control (Lee

et al. , 2008; Zhu et al.

et al. , 2005;