Polycomb

The third type of E3 ligases is represented by the polycomb protein 2 (Pc2), which was reported to enhance sumoylation of the substrate CtBP. N- and C-terminal domains in Pc2 that have been implicated in CtBP sumoylation do not resemble known E3 ligases. Like RanBP2, Pc2 expression is restricted to higher eukaryotes. 

Surprisingly, C. elegans appears to have lost a considerable number of chromatin proteins from the Polycomb group of proteins, observed in Drosophila and in mammals, although other transcription factor genes... 

Klymenko T, Papp B, Fischle W, Kocher T, Schelder M, Fritsch C, Wild B, Wilm M, Muller J (2006) A Polycomb group protein complex with sequence-specific DNA-binding and selective methyl-lysinebinding activities. Genes Dev 20 1110-1122... 

EPCl enhancer of polycomb 1. Subunit of the Tip60/NuA4 HAT complex. Physically links the Tip60-EPCl-ING3 trimer to the rest of the complex. Fused to PHFl/polycomb-like human protein in uterine sarcomas. 

Boyer LA, Plath K, Zeitlinger J, Brambrink T, Medeiros LA, Lee TI, Levine SS, Wernig M, Tajonar A, Ray MK et al (2006) Polycomb complexes repress developmental regulators in murine embryonic stem cells. Nature 19 April 441 349-353... 

Bracken AP, Dietrich N, Pasini D, Hansen KH, Helin K (2006) Genome-wide mapping of Polycomb target genes unravels their roles in cell fate transitions. Genes Dev 20 1123-1136... 

Varambally S, Dhanasekaran SM, Zhou M, Barrette TR, Kumar-Sinha C, Sanda MG, Ghosh D, Pienta KJ, Sewalt RG, Otte AP, Rubin MA, Chinnaiyan AM (2002) The polycomb group protein EZH2 is involved in progression of prostate cancer. Nature 419 624-629 Wade PA, Pruss D, Wolffe AP (1997) Trends Biochem Sci 22 128-132... 

Apart from this HDACs are also associated with a number of other epigenetic repression mechanisms including histone methylation, polycomb group of proteins and DNA methylation (discussed later). The class II HDACs have been found to be involved in muscle development, particularly HDAC 5 and 9 knockouts or mutants show evidence of cardiac hypertrophy in a age or stress dependent manner (Zhang et al, 2002 Chang et al, 2004). 

Mahmoudi T, Verrijzer CP (2001) Chromatin silencing and activation by Polycomb and trithorax group proteins. Oncogene 20 3055-3066... 

Kehle, J., Beuchle, D., Treuheit, S., Christen, B., Kennison, J.A., Bienz, M., and Muller, J. (1998) dMi-2, a Hunchback-interacting protein that functions in Polycomb repression. Science 282, 1897-1900. 

Pirrotta, V. (1997) PcG complexes and chromatin silencing. Curr. Opin. Genet. Dev. 7, 249-258. Poux, S., Horard, B., Sigrist, C.J.A., and Pirrotta, V. (2002) The Drosophila Trithorax protein is a coactivator required to prevent re-establishment of Polycomb silencing. Development 129, 2483-2493. 

Czermin, B., Melfi, R., McCabe, D., Seitz, V., Imhof, A., and Pirrotta, V. (2002) Drosophila Enhancer of Zeste/ESC complexes have a histone H3 methyltransferase activity that marks chromosomal Polycomb sites. Cell 111, 185-196. 

Essential for development [306]. Interacts with dHunchback protein. Functions in both Hunchback and Polycomb mediated repression in vivo [63] Interacts with the transcriptional repressor tramtrack69 [106]. 

Vire, E. et al. (2006) The Polycomb group protein EZH2 directly controls DNA methylation. Nature, 439, 871-874. 

Fischle, W, Wang, Y, Jacobs, S.A., Kim, Y, Allis, C.D. and Khorasanizadeh, S. (2003) Molecular basis for the discrimination of repressive methyl-lysine marks in histone H3 by Polycomb and HPl chromodomains. Genes and Development, 17, 1870-1881. 

Otte, A.P., Volkert, T.L., Bartel, D.P., Melton, D.A., Gifford, D.K., Jaenisch, R. and Young, R.A. (2006) Control of developmental regulators by Polycomb in human embryonic stem cells. Cell,... 

Orlando, V. and Paro, R. (1993) Mapping Polycomb-repressed domains in the bithorax complex using in vivo formaldehyde cross-linked chromatin. Cell, 75, 1187-1198. 

JARIDID - the least characterized JARIDl protein - was described to interact with Ring6a, a polycomb-like protein regulating expression of a polycomb target gene [75]. This could suggest overlapping functions between JARIDIA and JARIDID. 

Pasini, D., Hansen, K.H., Christensen, J., Agger, K., Cloos, P.A. and Helin, K. (2008) Coordinated regulation of transcriptional repression bythe RBP2 H3K4demethylase and Polycomb-Repressive Complex 2. Genes and Development, 22, 1345-1355. 

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