Transcriptional regulation of meiosis in budding yeast

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IV. Transcriptional regulation of early meiosis-specific genes (EMG) A. Silencing of early meiosis-specific genes in vegetative growth. In vegetative growth conditions with either glucose or acetate as the sole carbon source meiosisspecific genes are silent. Silencing of EMG is not only due to the absence of their main transcriptional activator, Ime1, but is rather due to active repression. The genes required to promote this silencing are WTM3, UME2, UME3, SIN3, RPD3, UME5, UME6, and ISW2 (Goldmark et al., 2000; Strich et al., 1989; Strich et al., 1994; Vidal and Gaber, 1991). Except for Ume6 and Isw2, these genes are not essential for the expression of EMG under meiotic conditions (Goldmark et al., 2000; Strich et al., 1989). 1. The WTM genes. UME1 (WTM3) and its two homologs WTM1 and WTM2 repress the transcription of the EMG IME2 synergistically (Pemberton and Blobel, 1997). These proteins also function as transcriptional repressors of the silent HMR cassette, and when tethered artificially to heterologous genes. These genes are non-essential; the wtm1 wtm2 wmt3 triple mutant is viable (Pemberton and Blobel, 1997). The Wtm proteins are expressed constitutively in both mitotic and meiotic conditions, and are localized to the nucleus (Pemberton and Blobel, 1997). The mode by which they cause repression is not known. 2. The UME2 gene. UME2 (SRB9, SSN2) is a component of the SRB subcomplex of RNA polymerase II holoenzyme (Kornberg, 1999). Although it is a negative regulator of EMG under vegetative growth conditions (Strich et al., 1989), when fused to lexA it activates transcription (Song and Carlson, 1998). 3. The UME3 and UME5 genes. The UME3 (SRB11, SSN8) and UME5 (SRB10, SSN3) encode integral components of the SRB subcomplex of RNA polymerase II holoenzyme (Cooper and Strich, 1998; Kornberg, 1999). UME3 encodes a cyclin C homolog that associates with the cyclin dependent kinase, Ume5 (Cooper et al., 1997; Cooper and Strich, 1998). Ume5 phosphorylates the C-terminal CTD repeats of RNA polymerase II, but this event is independent of its repression activity (Cooper and Strich, 1998), thus, it is not know how Ume5 represses the transcription of EMG. Ume3 is degraded in meiotic conditions, and this degradation, that is independent of Ume5, is required for complete relief of repression of EMG (Cooper et al., 1997). 19
4. The SIN3, UME6, and RPD3 genes. UME6 encodes a C6Zn2 protein that binds the URS1 sequence present in many genes including EMG (Anderson et al., 1995; Strich et al., 1994). The C6Zn2 domain is sufficient for binding, and is required for its repression activity (Anderson et al., 1995; Strich et al., 1994). Deletion of UME6 causes high expression of EMG, as well as additional non-meiotic genes carrying the URS1 element, in vegetative growth conditions (Bowdish and Mitchell, 1993; Lopes et al., 1993; Park et al., 1992; Strich et al., 1994). In addition, Ume6 functions as a transcriptional repressor when tethered to heterologous genes following its fusion to lexA (Kadosh and Struhl, 1997). This repression activity of Ume6 depends on the availability of Sin3 (Ume4, Rpd1) and Rpd3 (Kadosh and Struhl, 1997). Coimmunoprecipitation and two-hybrid assays demonstrate physical association between Ume6(515-530) and Sin3(426-472) (the PAH2 domain), as well as between Sin3 and Rpd3 (Kadosh and Struhl, 1997; Kasten et al., 1997; Washburn and Esposito, 2001). Sin3 functions as a transcriptional repressor when tethered to heterologous genes following its fusion to lexA (Wang and Stillman, 1993). The repression activity of Sin3 depends on Rpd3 (Kadosh and Struhl, 1997; Kasten et al., 1997). In accord, the double mutant sin3 rpd3 have the same phenotype as either single mutant (Vidal and Gaber, 1991). RPD3 encodes histone deacetylase whose deletion, similar to SIN3 deletion, causes an increase in acetylation of lysines 5 and 12 in histone H4 in various genes carrying the URS1 element (Burgess et al., 1999; Rundlett et al., 1998). Recruitment of the Sin3/Rpd3 complex by Ume6 to DNA results in decreased acetylation of histone H3 and H4 in a restricted region, up to two nucleosomes from the binding site of Ume6 (Kadosh and Struhl, 1998). 5. The ISW2 gene. Isw2 in a complex with Itc1 functions as an ATP dependent chromatinremodeling factor that is required for the repression of EMG under vegetative growth conditions (Goldmark et al., 2000). Isw2 functions in parallel to the Sin3/Rpd3 histone deacetylase complex, as deduced from the observation that the level of expression of EMG are dramatically increased in the sin3 isw2 double mutant in comparison to the single mutants (Goldmark et al., 2000). Isw2 physically associates with Ume6, and since it’s binding to the URS1 element depends on Ume6, it was concluded that Ume6 recruits the Isw2 complex to URS1 (Goldmark et al., 2000). DNaseI and micrococcal nuclease digestion of the chromatin near the EMG REC104 show dependence on Isw2, suggesting that the Isw2 complex forms an inaccessible chromatin structure near the URS1 element (Goldmark et al., 2000). These results suggest that Isw2 would be localized to the nucleus in vegetative growth media. However, this is not the case, Isw2 is localized to the cytoplasm in vegetative growth cultures, and to the nucleus, the cytoplasmic and spindle microtubuli, in meiotic cultures (Trachtulcova et al., 2000). There is no good explanation to 20
Page 1 and 2: Transcriptional regulation of meios
Page 3 and 4: 3. Proteins required for the associ
Page 5 and 6: I. Introduction The budding yeast S
Page 7 and 8: et al., 2000). On the other hand, i
Page 9 and 10: the UCS4 element upstream of the CY
Page 11 and 12: egulator of Cyr1, CDC25 encodes the
Page 13 and 14: 1998). Furthermore, unlike IREu, IR
Page 15 and 16: In the absence of glucose Sok2 does
Page 17 and 18: autophosphorylation, including on a
Page 19: hours in SPM, followed by a decline
Page 23 and 24: 1993). Nevertheless, when Ime1 is t
Page 25 and 26: However, direct demonstration of ph
Page 27 and 28: 3. Proteins required for the associ
Page 29 and 30: heterologous promoter does not supp
Page 31 and 32: expressed only in the absence of gl
Page 33 and 34: structure of hCDK2 reveals that cyc
Page 35 and 36: terminal non-essential domain (Komi
Page 37 and 38: is dependent on Ime2, but in cells
Page 39 and 40: VI. Transcriptional regulation of l
Page 41 and 42: The transcriptional activator that
Page 43 and 44: Functional interaction between Ime1
Page 45 and 46: Bowdish, K. S., and Mitchell, A. P.
Page 47 and 48: Foiani, M., Nadjar-Boger, E., Capon
Page 49 and 50: Jeffrey, P. D., Russo, A. A., Polya
Page 51 and 52: Lindgren, A., Bungard, D., Pierce,
Page 53 and 54: Pazin, M. J., and Kadonaga, J. T. (
Page 55 and 56: Shenhar, G. (2001). TRANSCRIPTIONAL
Page 57 and 58: Szent-Gyorgyi, C. (1995). A biparti
Page 59 and 60: Yoshida, M., Kawaguchi, H., Sakata,
Page 61 and 62: Fig. 4. The function of positive an
Page 63 and 64: Fig. 9. A schematic structure of IM
Page 65 and 66: activation by Ime2 is due to phosph
Page 67 and 68: MCK1 Protein kinase required for ef
Page 69: UME3 A cyclin C homolog that associ

Transcriptional regulation of meiosis in budding yeast

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