Transcriptional regulation of meiosis in budding yeast

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pathway is activated, the binding of Msn2/4 to Bmh2, the 14-3-3 adaptor, sequesters it from the nuclei (Beck and Hall, 1999). 3. The NLS site of Msn2 contains four PKA consensus sites. These residues are phosphorylated in vivo in response to glucose addition, depending on the presence of the three TPK genes. Serine to alanine mutations of all these sites lead to constitutive nuclear localization of Msn2, whereas serine to aspartic acid, mimicking a phosphorylated serine residue, leads to its cytoplasmic localization (Gorner et al., 2002). 1.1.2. Sok2. SOK2 encodes a DNA-binding protein that is highly homologous to the DNA-binding domain of Swi4 and Phd1 proteins that are known to bind the SCB consensus sequence. This homology suggests that Sok2 might also bind the same sequence. Direct binding of Sok2 to IREu was not reported, however, the following genetic evidence suggests that Sok2 binds IREu under all growth conditions. The IREu-his4-lacZ reporter shows a 10-fold increase in expression in the triple mutant sok2∆ msn2∆ msn4∆ in comparison to the double mutant msn2∆ msn4∆. On the other hand, IREu-his4-lacZ is not expressed in the sok2T598A msn2∆ msn4∆ triple mutant. The sok2T598A allele, similar to the SOK2 deletion allele is defective in repression, but unlike the latter, the defective Sok2 protein is present in the cells (Shenhar and Kassir, 2001). These results imply that Sok2 binds IREu under all growth conditions, and that in its physical absence an imposter protein can bind and activate transcription. Sok2 functions as a transcriptional repressor for several PKA target genes such as GAC1, SSA3, SWI5 and IME1 (Pan and Heitman, 2000; Shenhar and Kassir, 2001; Ward et al., 1995). Furthermore, it functions as a negative regulator of pseudohyphal growth (Ward et al., 1995) and meiosis (Shenhar and Kassir, 2001), and as a positive regulator in the mitotic cell cycle (Ward et al., 1995). Glucose regulates both the transcription of SOK2 and the repression activity of Sok2 protein. The latter is concluded from the observation that a Sok2-Gal4(bd), expressed from the ADH1 promoter, represses the transcription of UASGAL1-UASHIS4-his4-lacZ, but only in the presence of glucose (SD media) (Shenhar and Kassir, 2001). The signal pathway regulating the transcription of SOK2 is not known (Shenhar and Kassir, 2001). However, the signal pathway transmitting the glucose signal regulating Sok2 repression activity is the cAMP/PKA pathway. This is evident from the following observations: i. Over-expression of SOK2 suppresses the temperature sensitive growth defect of a tpk1∆ tpk2-ts tpk3∆ mutant (Ward et al., 1995); ii. Repression of IREu-his4-lacZ and UASgal1-UAShis4-his4-lacZ by either Sok2 or Gal4(bd)-Sok2, respectively, is relieved in cdc25- 5 cells incubated at the non-permissive temperature, as well as by a threonine to alanine mutation in a PKA consensus site in Sok2 (Shenhar and Kassir, 2001). Furthermore, Sok2 is a phosphoprotein whose phosphorylation depends on this same threonine (T598) residue (Shenhar and Kassir, 2001). 13
In the absence of glucose Sok2 does not repress transcription. Relief of repression in the absence of glucose depends on its N-terminal domain, amino acids 1-247 as well as on Ime1 [see section IIIE and (Shenhar and Kassir, 2001)]. The mode by which Sok2 represses transcription and how Ime1 relieves repression is not known. 1.2. Rim15. Rim15 encodes a serine/threonine protein kinase whose activity in glucose growth media is inhibited due to its phosphorylation by PKA (Reinders et al., 1998). In addition, the transcription of RIM15, and consequently the steady state level of Rim15, is increased in acetate growth media (Vidan and Mitchell, 1997). Diploid cells deleted for RIM15 or carrying a kinase-dead point mutation are sporulation deficient (Vidan and Mitchell, 1997). Deletion of RIM15 causes a drastic reduction in the transcription of IME1. The mode of action of Rim15, and the IME1 element regulated by it are not known. 2. The Snf1 signal-transduction pathway. SNF1 encodes a protein kinase whose activity as a kinase is inhibited in the presence of high levels of glucose (Jiang and Carlson, 1996). Snf1 function is required for the expression of glucose-repressed genes (Lesage et al., 1996). Snf1 phosphorylates the DNA-binding protein, Mig1 (Treitel et al., 1998) that recruits the Tup1/Ssn6 repression complex to the glucose-repressed genes to whom it binds (Nehlin et al., 1991). Snf1 is required for the high level induction in the transcription of IME1 in sporulation conditions, and diploid cells deleted for SNF1 arrest prior to premeiotic DNA replication, meiotic recombination, and spore formation (Honigberg and Lee, 1998). Over expression of either Msn2 or Msn4 suppresses a temperature sensitive allele of SNF1 (Estruch and Carlson, 1993), suggesting that Snf1 effect on IME1 might be mediated through Msn2/4. It is not known, though, whether Msn2/4 are direct targets of Snf1. Genetic evidence suggests that Snf1 is in a separate pathway than the cAMP/PKA pathway (Thompson-Jaeger et al., 1991), and both regulate Msn2/4. The sequence of IME1 shows no homology to the Mig1 binding site, and the region in IME1 regulated by Snf1 is not known. In the meiotic cycle Snf1 is also required following the transcription of IME1. When IME1 is placed on a multi-copy plasmid it is highly expressed in both wild type and snf1∆ diploid cells, nevertheless, in the SNF1 deleted strain over expressing Ime1, the EMG IME2 is only partially expressed, 10-15% of the cells complete premeiotic DNA replication and meiotic recombination, but spores are not formed (Honigberg and Lee, 1998). It was suggested that Snf1 is required in the meiotic cycle at three points, for the transcription of Ime1, for the transcription of Ime2, and for spore formation (Honigberg and Lee, 1998). 14
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: 1998). Furthermore, unlike IREu, IR
Page 17 and 18: autophosphorylation, including on a
Page 19 and 20: hours in SPM, followed by a decline
Page 21 and 22: 4. The SIN3, UME6, and RPD3 genes.
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
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