| الوصف: |
In eukaryotes, the strength of the interactions between the basic tails of the core histones and DNA can be modulated through post-translational modifications, such as acetylation (Strahl and Allis, 2000). Acetylation is catalyzed by histone acetyltransferases (HATs) and deacetylation is catalyzed by histone deacetylases (HDACs). Both enzyme classes exist in different multiprotein complexes and establish the state of histone acetylation that is correlated with the state of transcriptional activity and heterochromatinization (Ahringer, 2000; Lusser et al., 2001). In pea, histones were found to be hyperacetylated at the Pet E gene promoter, contributing to an open conformation but only when the gene is transcriptionally active (Chua et al., 2001). The HAT, Gcn5, was found to be targeted to the promoters of cold-responsive genes by the transcription factor, CBF-1, which modulates induction (Stockinger et al., 2001). Histone deacetylation was correlated with silencing of one parental set of rRNA genes in interspecific hybrids, a phenomenon known as nucleolar dominance (Chen and Pikaard, 1997). Corepressor complexes containing Polycomb-group proteins have been shown to play a role in regulating the spatial patterns of expression of floral and embryonic homeotic genes and it is believed that histone deacetylases play a key role in these complexes (Eshed et al., 1999; Ogas et al., 1999). |
