Thus, our testinvfragments will restore theenstripe pattern late in development only if they function similarly to theenPREs
Thus, our testinvfragments will restore theenstripe pattern late in development only if they function similarly to theenPREs. EachinvDNA fragment was inserted into the SD10 TAK 259 construct between the upstreamenregulatory DNA and theenpromoter, yielding SD10-invconstructs. the versatility of PREs despite discrepancies in the number and location of DNA binding sites. Polycomb group (PcG) genes encode a large group of conserved proteins that act on chromatin to repress transcription. Originally identified inDrosophila melanogasteras silencers of homeotic genes, PcG proteins act as transcriptional repressors for many diverse targets. PcG proteins act in multiple protein complexes to modify chromatin with marks typically associated with gene repression, including trimethylation of histone H3 at lysine 27 and ubiquitination of H2A at lysine 119 (for a review, see reference32). Histone deacetylases may also be involved. The exact protein complexes and mechanisms of PcG protein function are areas of intense investigation, with new complexes still being discovered (for a review, see recommendations32and38). Genetic evidence suggests that not all PcG proteins work on all targets (41), so it is usually probable that, in addition to having shared targets, different PcG protein complexes may regulate different genes. While all PcG proteins TAK 259 are specifically associated with chromatin, the only known PcG proteins with sequence-specific DNA binding activity are Pleiohomeotic (Pho) and the related protein Pho-like (Phol) (3,5). Pho is present in a complex with dSfmbt (Pho-RC) and is thought to play a key role in recruitment of other PcG protein complexes (24). InDrosophila, PcG proteins are recruited to specificcis-regulatory DNA elements called Polycomb response elements (PREs). These elements are typically found upstream of the transcript region and vary greatly in size and sequence (for a review, see reference31). Extensive analysis of PREs at a variety of genes, including the biothorax complex (BX-C) genes,engrailed(en),polyhomeotic(PH), as well as others, has revealed that PREs consist of multiple short motifs (34). DNA binding proteins TAK 259 implicated in PRE function include the GAGA factor (GAF) (42) and Pipsqueak (Psq) (27), which bind the same sequence, and Zeste (20,36), Pho (5,28), Sp1/Krppel-like factor (KLF) family members (4), DSP1 (9), and Grainyhead (Grh) (2). As mentioned previously, the Pho subunit of Pho-RC is usually a DNA binding protein and has been shown to be a central component of PREs and PcG protein function.In vitrobinding studies TAK 259 of the Pho protein and its mammalian homolog, YY1, have resulted in the generation of a core consensus sequence for Pho binding (GCCAT) (14,21,29). Recent chromatin immunoprecipitation (ChIP)-on-chip experiments have led to the development of longer, more stringent versions of the Pho consensus sequence TAK 259 (26,33). Once the Pho-RC complex is bound to PREs, it is believed to assist in actively recruiting the other PcG complexes to DNA, placing Pho in a role of great importance for the establishment of PcG-mediated silencing. While it is easy to speculate that Pho is usually a central component of PcG function, it is interesting that the removal of Pho consensus sequences from PREs does not always result in the complete loss of PcG-mediated silencing (4,5); furthermore, while Pho mutants exhibit phenotypes associated with Polycomb (PC), they are able to survive to the pharate adult stage (16). The identification of Phol, a factor with a high degree of homology Rabbit Polyclonal to PIGX to Pho and some degree of functional redundancy, helps explain why thephomutant phenotype is not more severe (3). Since deletion of any one individual DNA binding site often does not have a dramatic effect on PRE activity, it has been speculated that this multitude of binding sites work together to cooperatively recruit the factors necessary to establish gene silencing. Furthermore, it has been difficult to determine which combination of binding sites is required for PRE activity. To try and gain a better understanding of what key elements and binding sites may be.
