One possible model would be that histone post-translational modifications mark active transcription units and guide LEDGF/p75 binding.
As shown in Figure 2, histone modifications marking active transcription units and/or enhancers (all acetylations and H3K4 methylations) showed the strongest association (red shades in the heat map) with MLV integration sites.
MYC is often associated with histone modifications marking active genes (Nascimento et al., 2011; Rahl et al., 2010) and may therefore serve to amplify the program of gene expression dictated by other transcription factors.
In these studies, researchers discovered the combination of different histone modifications mark different chromatin states which often correspond to different genomic annotations such as promoters and enhancers [ 1, 11- 13].
Bivalent chromatin domains composed of both H3K4me3 and H3K27me3 modifications mark a large number of key regulators of lineage differentiation in ESCs in culture (Bernstein et al., 2006; Mikkelsen et al., 2007; Marks et al., 2012).
However, most of the histone modifications marking cis-regulatory regions occurred >50 kb away from genes with changed expression, suggesting that the enhancers may be far removed from the target gene.
Control experiments using the DHS-inhibitor GC7 revealed an almost complete inhibition of the hypusine modification, marked by the appearance of a third, even more acidic, signal.
However, the silencing H3K27me3 modification marked a vast majority of transcription factors involved in development or lineage decision in other cell types.
We next examined the possible functions of this histone modification marking system.
Furthermore, in both of these phases, histone modification marking distinguishes canonical exons from alternatively-spliced exons, both of which are seen as distinct from introns.
