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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Full expression <strong>of</strong> Ime1 <strong>in</strong> S288C stra<strong>in</strong>s deleted for RME1 or UCS3 and UCS4 does not lead<br />
to complete sporulation (Kassir et al., 1988; Sagee et al., 1998), suggest<strong>in</strong>g that the Mata1 Matα2<br />
prote<strong>in</strong>s might be required for a downstream meiotic event. On the other hand, <strong>in</strong> SK1<br />
background, this is not the case, and the MATa1 and MATα2 alleles are required only for the<br />
transcription <strong>of</strong> IME1 (Covitz and Mitchell, 1993). There are many reported cases <strong>of</strong> phenotypic<br />
differences between SK1 and other stra<strong>in</strong>s, i.e. S288C or W303. Genomic DNA hybridization<br />
reveals the presence <strong>of</strong> many deletions and polymorphisms between these stra<strong>in</strong>s (Primig et al.,<br />
2000). Thus, the discrepancy between results is attributed to the absence <strong>of</strong> some functions <strong>in</strong> the<br />
different stra<strong>in</strong>s.<br />
1. Genes whose products transmit the MAT signal to IME1 and <strong>meiosis</strong>. Three<br />
genes are known to transmit the MAT signal to IME1 and <strong>meiosis</strong>: RME1, IME4, and RES1.<br />
1.1. RME1. RME1 encodes a Z<strong>in</strong>c-f<strong>in</strong>ger DNA-b<strong>in</strong>d<strong>in</strong>g prote<strong>in</strong> (Covitz et al., 1991;<br />
Shimizu et al., 1997a) that is a negative regulator for the transcription <strong>of</strong> IME1 and <strong>meiosis</strong> <strong>in</strong><br />
cells carry<strong>in</strong>g only one <strong>of</strong> the MAT alleles (Kassir et al., 1988; Kassir and Simchen, 1976;<br />
Mitchell and Herskowitz, 1986; R<strong>in</strong>e et al., 1981). Recessive mutations <strong>in</strong> RME1 and deletion <strong>of</strong><br />
RME1 lead to complete expression <strong>of</strong> IME1 and sporulation <strong>in</strong> mata1/MATα, MATa/MATa and<br />
MATα/MATα stra<strong>in</strong>s (Kassir et al., 1988; Kassir and Simchen, 1976; Mitchell and Herskowitz,<br />
1986). Haploid cells carry<strong>in</strong>g the rme1-1 mutation complete premeiotic DNA replication, but<br />
arrest as mono nucleate cells without loss <strong>of</strong> viability (Kassir and Simchen, 1976). This is most<br />
probably due to the pachytene checkpo<strong>in</strong>t mechanism that monitors lack <strong>of</strong> synapsis and/or<br />
recomb<strong>in</strong>ation [for review on this checkpo<strong>in</strong>t see (Roeder and Bailis, 2000)]. In MATa/MATα<br />
stra<strong>in</strong>s relief <strong>of</strong> repression is due to the substantial reduction (10 to 20-fold) <strong>in</strong> the level <strong>of</strong> RME1<br />
mRNA and prote<strong>in</strong> [(Mitchell and Herskowitz, 1986), and L. Johnston, personal communication].<br />
The Mata1/Matα2 complex b<strong>in</strong>ds to a specific element <strong>in</strong> the promoter <strong>of</strong> RME1 repress<strong>in</strong>g its<br />
transcription (Goutte and Johnson, 1988; Johnson and Herskowitz, 1985; Li et al., 1995; Stark<br />
and Johnson, 1994).<br />
Rme1 b<strong>in</strong>ds the IME1 5’ region to two sites localized with<strong>in</strong> UCS4, at -2040 to –2030 and –<br />
1959 to –1949 (Shimizu et al., 1998). The consensus sequence for b<strong>in</strong>d<strong>in</strong>g is GWACCTCAARA<br />
(Shimizu et al., 1998). The presence <strong>of</strong> these two b<strong>in</strong>d<strong>in</strong>g sites; def<strong>in</strong>ed as the RRE and the<br />
modulation element (Covitz and Mitchell, 1993), is required to repress the transcription <strong>of</strong> IME1.<br />
Deletion or mutations <strong>in</strong> a s<strong>in</strong>gle site cause only partial derepression (Shimizu et al., 1998).<br />
Moreover, deletion <strong>of</strong> both sites does not lead to complete relief <strong>of</strong> repression, (Shimizu et al.,<br />
1998), probably due to the repression activity <strong>of</strong> the UCS3 site (Sagee et al., 1998). Insertion <strong>of</strong><br />
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