Transcriptional regulation of meiosis in budding yeast

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clarify these contradicting results. Isw2 is required for meiosis, cells deleted for ISW2 arrest under meiotic conditions prior to premeiotic DNA replication, and asci are not formed (Trachtulcova et al., 2000). It is not known whether Isw2 is required for the transcription of EMG under meiotic conditions, nor why cells deleted for ISW2 are sporulation deficient. B. Expression of early MSG under meiotic conditions. 1. Ume6 is also a positive regulator. Ume6 is required for the transcription of EMG under meiotic conditions (Bowdish and Mitchell, 1993; Bowdish et al., 1995; Steber and Esposito, 1995; Strich et al., 1994; Szent-Gyorgyi, 1995). In addition, Sin3 and Rpd3 are required for their high level of expression (Lamb and Mitchell, 2001). Ume6, Sin3 and Rpd3 are present and physically associate in both vegetative growth and meiotic conditions (Lamb and Mitchell, 2001). When tethered to heterologous genes, Ume6 can serve as either a transcriptional repressor or activator, depending on Sin3/Rpd3 and Ime1, respectively (Bowdish et al., 1995; Kadosh and Struhl, 1997). Different domains in Ume6 are required for transcriptional repression and activation (Bowdish et al., 1995; Washburn and Esposito, 2001). The Ume6T99N mutant protein is competent in repression of EMG in growth conditions, but is defective in their expression under meiotic conditions (Bowdish et al., 1995). On the other hand, the M530T mutation in UME6 has a defect only in repression (Washburn and Esposito, 2001). In agreement, the transcriptional activator, Ime1 associates with Ume6(1-232) (Rubin-Bejerano et al., 1996), while the transcriptional repressor, Sin3, with Ume6(515-530) (Kadosh and Struhl, 1997; Kasten et al., 1997; Washburn and Esposito, 2001). The positive and negative roles of Ume6 are mediated through its binding to the URS1 element whose presence is required for complete expression of EMG in starved cells (Bowdish et al., 1995). 2. The function of Ime1. IME1 encodes as positive regulator of meiosis. Over-expression of Ime1 bypasses the requirement for MATa1 and MATα2 gene products for sporulation (Kassir et al., 1988). Diploid cells deleted for IME1 arrest under meiotic conditions in G1, as unbudded cells (Foiani et al., 1996; Kassir et al., 1988), prior to execution of any meiotic event, namely, expression of meiosis-specific genes, premeiotic DNA replication, commitment to meiotic recombination, meiotic divisions, and spore formation (Foiani et al., 1996; Kassir et al., 1988; Mitchell et al., 1990; Smith and Mitchell, 1989). The requirement of IME1 for transcription suggests that it might encode a transcription factor. However, its predicted amino acid sequence does not show any homology to known DNA-binding motifs (Sherman et al., 1993; Smith et al., 21
1993). Nevertheless, when Ime1 is tethered to heterologous genes it functions as a potent transcriptional activator (Mandel et al., 1994; Smith et al., 1993). As described above, the transcription of IME1 is subject to extensive regulation by the MAT alleles and nutrients. On top of it, translation of IME1 mRNA is regulated by nutrients (Sherman et al., 1993). In vegetative growth media with acetate as the sole carbon source low but substantial levels of IME1 or ime1-lacZ mRNAs are observed, but Ime1-lacZ protein is not detected. On the other hand, upon nitrogen depletion, the level of IME1 mRNA is not induced in MATa/MATa cells, but Ime1-lacZ protein is readily observed (Sherman et al., 1993). Furthermore, α-factor and heat-shock treatment increases the transcription of IME1, but translation occurs only in cells arrested in G1 by either α-factor, or the CDC mutations cdc28-4 and cdc4-3 (Sherman et al., 1993). These results suggest that nitrogen and/or cell cycle progression inhibits translation of IME1 mRNA. Since nitrogen depletion leads to a G1 arrest, it is possible that the effect of nitrogen is indirect, and that a G1 arrest is a prerequisite for efficient translation. IME1 has an atypical 5 UTR (untranslated region), 229 bp long (Sherman et al., 1993), which might mediate this regulation. Sequence analysis reveals that this RNA region can form stem-and-loop secondary structure that might inhibit translation. However, deletion of this region has no effect on the translation of IME1 mRNA (Ben- Dov, 1994). Thus, it is not known how nitrogen and/or G1 phase controls the efficiency of translation of IME1 mRNA. Over expression of Ime1 in acetate growth media does not induce meiosis and sporulation in logarithmic cultures of wild-type diploids (Colomina et al., 1999; Sherman et al., 1993). On the other hand, in diploid cells arrested in G1 by recessive temperature sensitive mutations in CDC28, CDC4, CDC25, CDC35 (CYR1), or concomitant deletion of the three CLN genes, high percentages of asci are formed (Colomina et al., 1999; Sherman et al., 1993; Shilo et al., 1978), suggesting that post-translational modification of Ime1 or another factor required for meiosis depends on lack of function of these proteins. Indeed, in vegetative cultures, depending on the Cdc28/Cln function, Ime1 is phosphorylated and sequestered from the nucleus (Colomina et al., 1999). The localization of Ime1 in the cytoplasm prevents its transcriptional activation function, and entry into meiosis. Cdc4 is an F-box protein [for review see (Patton et al., 1998)] required for degradation of specific targets in G1. Interestingly, one of its substrates is Far1, an inhibitor of Cln/Cdc28 function (Henchoz et al., 1997). Thus, the effect of Cdc4 on sporulation may be mediated through Cdc28/Cln function. The role of Cdc25 and Cdc35, the two positive regulators of PKA on the function of Ime1 is most probably through their effect on the association of Ime1 with Ume6 (see below). 22
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 and 20: hours in SPM, followed by a decline
Page 21: 4. The SIN3, UME6, and RPD3 genes.
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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