Biology Reference
In-Depth Information
cycle expression during S phase, frustratingly, the transcription factors have
eluded characterization (Freeman
, 1992). However, global transcription
factor binding experiments have indicated that SBF binds to histone promoters
(Iyer
et al.
et al.
, 2001), so it may have a role in the regulation of their expression
(Simon
, 2001). Furthermore, two potential transcriptional repressors have
been identified, and named Hir1p and Hir2p (Sherwood
et al.
et al.
, 1993; Spector
et al.
, 1997).
Another wave of gene expression during S phase is controlled by the
Hcm1p forkhead-like transcription factor (Pramila
, 2006), which belongs
to a class of conserved transcription factors found throughout the animal king-
dom, all containing a so-called
et al.
forkhead DNA-binding motif
(Carlsson and
Mahlapuu, 2002; Durocher and Jackson, 2002; Durocher
et al.
, 1999;
Kaufmann and Kn
ยจ
chel, 1996). The
gene is transcribed during G1-S
under both MBF and SBF controls (Rowicka
HCM1
, 2007). In addition to
activating S-phase expression of genes involved in budding and chromosome
segregation, Hcm1p controls expression of Whi5p, repressing G1-S transcription
in the following cycle. It also activates
et al.
, which represses ECB elements
later in the cycle (Section II.A.4). In addition, Hcm1p also directly controls the
transcription of
YHP1
that encode transcription factors
which control G2-M transcription. Thus, this transcription factor has a central
role in cell cycle controls, regulating gene expression both directly and indirectly
throughout the cell cycle.
FKH1
,
FKH2
, and
NDD1
3. G2-M waves
The G2-M phase in budding yeast is a major cell cycle transition in this
organism, and correspondingly a large group of cell cycle regulated genes,
sometimes known as the CLB2 cluster, is expressed exclusively at this time.
The pioneer gene in this class was
, with Mcm1p identified as the tran-
scription factor that controls its expression and the rest of the group (Althoefer
et al.
SWI5
, 1995; Lydall
et al.
, 1991; Maher
et al.
, 1995). Mcm1p is a member of a class
of so-called
that are found in all eukaryotic
organisms, from yeasts to humans, where it is known as serum response factor
(Shore and Sharrocks, 1995; Treisman, 1994; Wynne and Treisman, 1992).
Mcm1p had been much studied in budding yeast and shown to have many
roles in controlling gene expression of a range of genes, including those for
mating-type switching (Gelli, 2002). The ability of Mcm1p to control various
groups of gene expression occurs through it having differing binding partners that
confer specificity, and is the modus operandi of MADS box proteins in all
organisms (Acton
MADS box transcription factors
et al.
, 1997; Messenguy and Dubois, 2003; Tuch
et al.
, 2008a).
