Transcriptional regulation of meiosis in budding yeast
Transcriptional regulation of meiosis in budding yeast
Transcriptional regulation of meiosis in budding yeast
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4, l<strong>in</strong>es F,G,H), confirm<strong>in</strong>g their function as UAS elements (Sagee et al., 1998; Shenhar and<br />
Kassir, 2001). In addition, <strong>in</strong> the presence <strong>of</strong> glucose UASru and IREu function as repression<br />
elements [Fig. 4, l<strong>in</strong>es F,G and (Shenhar and Kassir, 2001)]. Deletion <strong>of</strong> UASru <strong>in</strong>creases<br />
expression <strong>in</strong> SD, but <strong>in</strong> SA or SPM expression is absent (Fig. 4, l<strong>in</strong>e F), suggest<strong>in</strong>g that UASru<br />
functions as a URS element <strong>in</strong> the presence <strong>of</strong> glucose and as a UAS element <strong>in</strong> the absence <strong>of</strong><br />
glucose and/or the presence <strong>of</strong> acetate. Nested deletion <strong>of</strong> IREu leads to the same levels <strong>of</strong><br />
expression <strong>of</strong> ime1-lacZ <strong>in</strong> both SD and SA media [Fig. 4, l<strong>in</strong>e G, (Sagee et al., 1998)],<br />
suggest<strong>in</strong>g that its URS activity is regulated by either the carbon or nitrogen source. These<br />
UASru, IREu and UASrm element function as a carbon source regulated UAS when <strong>in</strong>serted<br />
upstream <strong>of</strong> a his4-lacZ reporter gene (Fig. 6). Decreased levels <strong>of</strong> expression are observed <strong>in</strong> SD,<br />
and <strong>in</strong>creased expression is observed <strong>in</strong> SA, while <strong>in</strong> SPM there is a slight <strong>in</strong>crease <strong>in</strong> activity, but<br />
only <strong>in</strong> the presence <strong>of</strong> UASru [Fig. 6 and (Sagee et al., 1998)]. These results imply that IREu and<br />
UASrm are regulated only by the glucose signal, and that UASru is ma<strong>in</strong>ly regulated by glucose<br />
but nitrogen has also a partial effect on its activity.<br />
1. The cAMP/PKA signal-transduction pathway. Genetic analysis suggests that the<br />
cAMP/PKA signal pathway transmits a nitrogen signal [see section IIIB and (Gancedo, 2001; Pan<br />
et al., 2000)]. However, biochemical and genetic analysis demonstrate that this pathway is one <strong>of</strong><br />
the major signal transduction pathways transmitt<strong>in</strong>g a glucose signal to <strong>yeast</strong> cells. This is an<br />
essential pathway that transiently <strong>in</strong>creases the level <strong>of</strong> cAMP <strong>in</strong> response to glucose addition [for<br />
reviews see (Broach, 1991; Thevele<strong>in</strong> and de W<strong>in</strong>de, 1999)]. Addition <strong>of</strong> 10mM cAMP to diploid<br />
cells <strong>in</strong>cubated <strong>in</strong> sporulation conditions leads to a small but significant reduction <strong>in</strong> the<br />
expression <strong>of</strong> IME1 and the level <strong>of</strong> sporulation (Fig. 7). The expression <strong>of</strong> either UASrm-his4lacZ<br />
or UASru-his4-lacZ is slightly <strong>in</strong>creased by addition <strong>of</strong> cAMP. However, about 1.6-fold<br />
reduction <strong>in</strong> the expression <strong>of</strong> IREu-his4-lacZ is observed, similar to the effect cAMP has on<br />
sporulation and IME1 expression, suggest<strong>in</strong>g that the activity <strong>of</strong> IREu is negatively regulated by<br />
cAMP. The signal transduction pathways that transmit the glucose signal to UASru and UASrm<br />
are not known.<br />
1.1. The IREu element. The sequence <strong>of</strong> IREu (-1153 to –1121) reveals that it <strong>in</strong>cludes<br />
two known positive elements, a stress response element, STRE, and the Swi4/Swi6 cell cycle<br />
box, SCB (Fig. 8). An almost identical element, IREd, is present at –788 to –756 <strong>of</strong> IME1 (Fig.<br />
3). IREd differs from IREu <strong>in</strong> two residues localized to the STRE and SCB elements (Fig. 8). An<br />
ime1-lacZ chimeras whose 5’ end are term<strong>in</strong>ated downstream or upstream <strong>of</strong> either IREu or IREd<br />
show that IREu functions as a positive element, whereas IREd as a negative element (Sagee et al.,<br />
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