Transcriptional regulation of meiosis in budding yeast

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involved with the nuclear cell cycle are required for meiosis (Simchen, 1974), and are expressed in both the mitotic and meiotic cycles. The RAD genes are involved with DNA repair as well as in checkpoint surveillance, and in meiosis are required for meiotic recombination and surveillance mechanisms. Initiation and progression through the meiotic cycle is regulated by a transcriptional cascade consisting of a temporal and programmed expression of 6 classes of meiosis-specific genes (early I, early II, early middle, middle, mid-late, and late) (Chu et al., 1998; Primig et al., 2000). Fig. 2 shows a schematic drawing of this transcriptional cascade, the timing of meiotic events, and the input of the meiotic signals. IME1 is the master regulator gene absolutely required for entry into the meiotic cycle and the transcription of all meiosis-specific genes (Kassir et al., 1988; Smith and Mitchell, 1989). Briefly, in the mitotic cell cycle IME1 is silent, as its transcription is regulated by the three meiotic signals (Kassir et al., 1988). The translation and activity of Ime1 is also regulated by nutrients (Rubin-Bejerano et al., 1996; Sherman et al., 1993). IME1 encodes a transcriptional activator that is directly required for the transcription of early meiosis-specific genes (EMG) (Mandel et al., 1994; Smith et al., 1993). The transcription of the middle genes (MMG) depends on the transcription factor, Ndt80, and on the serine/threonine protein kinase, Ime2, two early meiosis-specific genes whose transcription depends on Ime1 (Chu and Herskowitz, 1998; Hepworth et al., 1998; Mitchell et al., 1990; Yoshida et al., 1990). In addition, the function of Ime2 is directly regulated by nutrients (Donzeau and Bandlow, 1999; Mitchell et al., 1990; Yoshida et al., 1990). Transcriptional regulation of mid-late and late genes (LMG) is less clear, however, their regulated expression depends on the upstream regulators, Ime1, Ime2, and Ndt80, as well as on nitrogen depletion (Friesen et al., 1997; Kihara et al., 1991). There is a good correlation between time of transcription and meiotic function (Chu et al., 1998; Primig et al., 2000). The transcription of EMG is induced prior to premeiotic DNA replication, and it includes genes required for pairing of homologous chromosomes (i.e. HOP1), and meiotic recombination (i.e. DMC1). Furthermore, the transcription of CDC genes required for premeiotic DNA replication is induced at this time (i.e. POL1) (Johnston et al., 1986). Middle genes are induced following completion of DNA replication and prior to the first nuclear division. These genes are involved with nuclear division (i.e. CLB1,3,4, CDC26). The late genes are expressed following completion of nuclear divisions, and are involved with spore formation and its maturation (i.e. DIT1, SPS100) (Chu et al., 1998). However, some genes don’t follow this rule. For example, CLB5,6 are middle genes (Chu et al., 1998) that are required for premeiotic DNA replication (Dirick et al., 1998; Stuart and Wittenberg, 1998). In the mitotic cell cycle Clb5 is also required for spindle orientation, a process occurring concomitantly with DNA replication (Segal 5
et al., 2000). On the other hand, in the meiotic cycle, separation of the duplicated Spindle-Pole Bodies and spindle formation occur following completion of DNA replication (Goetsch and Byers, 1982). It seems, therefore, that the transcription of CLB5/6 correlates with their second putative meiotic function. III. Transcriptional regulation of IME1. The different signal pathways that lead to meiosis converge at IME1, promoting its transcription (Kassir et al., 1988). In vegetative growth media with glucose as the sole carbon source (SD - synthetic dextrose) IME1 is not transcribed. A low basal level of IME1 mRNA is present in growth media when acetate is the sole carbon source (SA - synthetic acetate) (Kassir et al., 1988). Upon nitrogen depletion and the presence of acetate (SPM - sporulation media), the level of IME1 mRNA is transiently increased in MATa/MATα diploids, but not in cells carrying only a single active MAT allele (Kassir et al., 1988). In addition, IME1 is subject to both positive and negative feedback regulation (Shefer-Vaida et al., 1995). An extremely large region, about 2.1 kb long, consisting of distinct positive and negative elements mediates the regulated transcription of IME1 (Granot et al., 1989; Sagee et al., 1998; Sherman et al., 1993; Smith et al., 1990). By deletion analysis and insertion of specific elements of IME1 in heterologous reporter genes, the meiotic signals affecting discrete elements were identified (Fig. 3) (Covitz and Mitchell, 1993; Sagee et al., 1998; Sherman et al., 1993; Smith et al., 1990). Below is a detailed review on how the MAT, Glucose, and Nitrogen signals are transmitted to IME1. A. The MAT signal The MAT signal is transmitted through two distinct elements, UCS3 and UCS4, which do not share any sequence homology (Covitz and Mitchell, 1993; Sagee et al., 1998). Deletion of any of these elements leads to partial derepression, whereas deletion of both elements results in full expression of IME1 in MATa/MATa cells (Sagee et al., 1998). In addition, UCS3 is apparently required for complete relief of repression of UCS4. Nested deletion of UCS3 leads to a 2-fold reduction in the expression of ime1-lacZ in MATa/MATα cells incubated under meiotic conditions, whereas in concomitant deletion of UCS4 and the entire upstream region, the expression of ime1-lacZ is complete (Fig. 4, compare line B to lines A and C). The proteins through which MAT regulation is transmitted to UCS3 are not known. As discussed below, Rme1 transmits the MAT signal to UCS4 (Covitz and Mitchell, 1993) (see section IIIA1.1). 6
Page 1 and 2: Transcriptional regulation of meios
Page 3 and 4: 3. Proteins required for the associ
Page 5: I. Introduction The budding yeast S
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 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
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Szent-Gyorgyi, C. (1995). A biparti
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Yoshida, M., Kawaguchi, H., Sakata,
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Fig. 4. The function of positive an
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Fig. 9. A schematic structure of IM
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activation by Ime2 is due to phosph
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MCK1 Protein kinase required for ef
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UME3 A cyclin C homolog that associ
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Transcriptional regulation of meiosis in budding yeast

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