Transcriptional regulation of meiosis in budding yeast

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1.2. IME4. IME4 encodes a positive regulator absolutely required for the transcription of IME1 (Shah and Clancy, 1992). The transcription of IME4 is regulated by the meiotic signals; it requires the presence of the MATa1 and MATα2 gene products and nitrogen depletion. Rme1 does not transmit the MAT signal to IME4 (Shah and Clancy, 1992), suggesting that Rme1 and Ime4 function in two distinct signal pathways. The region within IME1 responding to Ime4, and the mode by which Ime4 activates the transcription of IME1 is not known. Over expression of Ime1 partially suppresses ime4∆, suggesting that Ime4 have an additional role in meiosis (Shah and Clancy, 1992). Ime4 associates with Mum2/SpoT-8 (Uetz et al., 2000) that is required for premeiotic DNA replication (Engebrecht et al., 1998; Tsuboi, 1983). It is possible that the second meiotic function of Ime4 is to regulate the function of this protein. 1.3. RES1. The dominant mutation Res1-1 bypasses the requirement for the presence of both Mata1 and Matα2 for the expression of IME1 and meiosis (Kao et al., 1990). Res1-1 is not allelic to RME1, IME1 or IME4 (Kao et al., 1990; Shah and Clancy, 1992), neither is Res1 in the Ime4 or Rme1 signal pathway (Kao et al., 1990; Shah and Clancy, 1992). This gene has not been cloned, and its normal function is not known. B. The nitrogen signal The nitrogen signal is transmitted to IME1 through the UCS1 element (Fig. 3). Nested deletion of this region leads to a 5 and 15-fold increase in the expression of ime1-lacZ in vegetative growth media with either glucose (SD) or acetate (SA) as the sole carbon source, respectively [Fig. 4, compare lines D and E, (Sagee et al., 1998)]. These results suggest that UCS1 functions as a negative element in the presence of glucose and nitrogen. By itself UCS1 has no UAS activity, it cannot promote expression of a his4-lacZ reporter gene lacking its own UAS (Nadjar-Boger, 2000). Insertion of UCS1 between the HIS4 UAS and TATA box in the HIS4UAS-HIS4TATA-lacZ reporter gene leads to a substantial reduction of expression in SD and SA [Fig. 5, (Sagee et al., 1998)]. Level of repression is 2 to 3-fold higher in SD in comparison to SA, confirming that the activity of UCS1 is partially regulated by glucose. Upon nitrogen depletion (SPM) a substantial increase in expression is observed [Fig. 5 and (Sagee et al., 1998)], suggesting that nitrogen is the major signal regulating the function of UCS1. The cAMP/PKA pathway transmits a nitrogen signal to IME1 and meiosis (Matsumoto et al., 1983; Matsuura et al., 1990). Mutations that cause low or no activity of PKA, such as cyr1, ras2, and cdc25 lead to the expression of IME1 and spore formation in the presence of nitrogen (Matsumoto et al., 1983; Matsuura et al., 1990; Shilo et al., 1978; Smith and Mitchell, 1989) [CYR1 encodes adenylate cyclase, RAS2 encodes a small G protein that functions as a positive 9
egulator of Cyr1, CDC25 encodes the Ras GDP/GTP exchange factor, which serves as a positive regulator of adenylate cyclase (Broach, 1991; Broek et al., 1987; Toda et al., 1985)]. On the other hand, mutations that cause constitutive PKA activity, such as RAS2-val19 (activated Ras) and bcy1 [the regulatory subunit of PKA (Broach, 1991)] are sporulation deficient, and are suppressed by over-expression of IME1 (Matsuura et al., 1990). The repression activity of UCS1 is reduced in vegetatively grown cdc25-5 cells incubated at the non-permissive temperature (Fig. 5). Upon nitrogen depletion (SPM), this phenomenon is not observed; the same levels of expression are observed in cells incubated at the permissive or restrictive temperature (Fig. 5). These results suggest that Cdc25 transmits the nitrogen signal to UCS1. Cdc25 is a positive regulator of both the, cAMP/PKA (Broek et al., 1987) and MAPK (Shenhar, 2001) signal transduction pathways. Therefore, further experiments are required to determine if this effect of Cdc25 is mediated through PKA, MAPK or a different signal pathway. MDS3 and its homologue, PMD1, are negative regulators of IME1 transcription in vegetative growth media with acetate as the sole carbon source. Deletion of these genes results in an increase in the transcription of IME1 and the EMG IME2 and HOP1 (Benni and Neigeborn, 1997). In addition, when stationary phase mds3∆ pmd1∆ diploid cells are shifted from SD to SA media, growth is ceased and about 10% of the cells enter and complete the meiotic cycle. These results suggest that Mds3/Pmd1 function upstream of Ime1, in preventing cell cycle arrest in the presence of nitrogen (Benni and Neigeborn, 1997). Growth arrest and sporulation are suppressed in cells carrying the RAS2-val19 mutation, suggesting that these genes might be upstream activators of the Ras pathway (Benni and Neigeborn, 1997). The region in IME1 that is regulated by these genes is not known. It will be interesting to determine if their effect is mediated through the UCS1 element. As discussed above, the Mata1 and Matα2 gene products are required to induce expression in the absence of nitrogen, suggesting that UCS1 might also mediate the MAT signal. However, the repression activity of UCS1 and its relief (in a UASHIS4-UCS1-his4-lacZ reporter) is identical in isogenic haploid and diploid cells (Boger-Nadjar, 2000), indicating that the activity of UCS1 is not regulated by MAT. However, it is still possible that within the context of IME1 promoter, UCS1 might interact with the UCS3 and/or UCS4 elements that mediate MAT regulation. C. The glucose Signal The UAS activity of IME1 is confined to UCS2, a region that contains alternate positive and negative elements [Fig. 3, (Sagee et al., 1998)]. Nested deletions of either one of its three positive elements, UASru, IREu, and UASrm lead to a reduction in expression of ime1-lacZ in SPM (Fig. 10
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: the UCS4 element upstream of the CY
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
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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Transcriptional regulation of meiosis in budding yeast

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