The divergently transcribed DIT1 and DIT2 genes of Saccharomyces cerevisiae, which belong to the mid-late class of sporulation-specific genes, are subject to Ssn6-Tup1-mediated repression in mitotic cells. The Ssn6-Tup1 complex, which is required for repression of diverse sets of coordinately regulated genes, is known to be recruited to target genes by promoter-specific DNA-binding proteins. In this study, we show that a 42-bp negative regulatory element (NRE) present in the DIT1-DIT2 intergenic region consists of two distinct subsites and that a multimer of each subsite supports efficient Ssn6-Tup1-dependent repression of a CYC1-lacZ reporter gene. By genetic screening procedures, we identified DFG16, YGR122w, VPS36, and the DNA-binding proteins Rim101 and Nrg1 as potential mediators of NRE-directed repression. We show that Nrg1 and Rim101 bind simultaneously to adjacent target sites within the NRE in vitro and act as corepressors in vivo. We have found that the ability of Rim101 to be proteolytically processed to its active form and mediate NRE-directed repression not only depends on the previously characterized RIM signaling pathway but also requires Dfg16, Ygr122w, and components of the ESCRT trafficking pathway. Interestingly, Rim101 was processed in bro1 and doa4 strains but was unable to mediate efficient repression.The yeast Saccharomyces cerevisiae can respond to changes in nutrient availability and environmental conditions by switching from one growth form to another. Extracellular cues are interpreted by various signal transduction pathways that act by both independent and convergent mechanisms to coordinate morphogenetic events. The different regulatory cascades and the interplay between them ultimately modulate the activity of target transcription factors and progression through the cell cycle. Haploid cells that are starved for glucose and diploid cells that are starved for nitrogen switch from growth as single budding cells to growth as long filaments of connected cells, with haploid cells becoming particularly adept at invasive growth and penetration into solid agar medium (reviewed in reference 63). Starvation of a diploid MATa/MAT␣ cell for an essential nutrient in the absence of glucose and in the presence of a nonfermentable carbon source directs the cell into the pathway for spore formation (reviewed in reference 40). The nutritional signaling leads to arrest of the starved cell at G 1 and contributes in a diploid to the expression of two key regulatory genes, IME1 and IME2, which encode a transcriptional activator and a protein kinase, respectively (reviewed in reference 43). These regulators set in motion the sporulation program that consists of meiotic DNA replication, recombination, the two meiotic divisions, and encapsulation of each haploid nucleus within a multilayered spore wall (reviewed in reference 48). This coordinated series of genetic and morphological events depends on the sequential expression of temporally distinct classes of sporulation-specific genes (18, 68).The regulated...
Genes of the Polycomb group maintain long-term, segment-specific repression of the homeotic genes in Drosophila. DNA targets of Polycomb group proteins, called Polycomb response elements (PREs), have been defined by several assays, but they have not been dissected in their original chromosomal context. An enhanced method of gene conversion was developed to generate a series of small, targeted deletions encompassing the best-studied PRE, upstream of the Ultrabithorax (Ubx) transcription unit in the bithorax complex. Deletions that removed an essential 185-bp core of the PRE caused anterior misexpression of Ubx and posterior segmental transformations, including the conversion of the third thoracic segment toward a duplicate first abdominal segment. These phenotypes were variable, suggesting some cooperation between this PRE and others in the bithorax complex. Larger deletions up to 3 kb were also created, which removed DNA sites reportedly needed for Ubx activation, including putative trithorax response elements. These deletions resulted in neither loss of Ubx expression nor loss-of-function phenotypes. Thus, the 3-kb region including the PRE is required for repression, but not for activation, of Ubx.bithorax ͉ Ultrabithorax ͉ gene conversion
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