Histone modifications not only play important roles in regulating chromatin structure and nuclear processes but also can be passed to daughter cells as epigenetic marks. Accumulating evidence suggests that the key function of histone modifications is to signal for recruitment or activity of downstream effectors. Here, we discuss the latest discovery of histone-modification readers and how the modification language is interpreted.

PICH and BLM limit histone association with anaphase centromeric DNA threads and promote their resolutionThe helicase proteins PICH and BLM localize to ultrafine DNA threads between separating sister chromatids. It now appears they cooperate to remove histones from these anaphase DNA bridges, to allow their stretching and unravelling without breakage.

Gene expression requires the recruitment of chromatin remodeling activities and general transcription factors (GTFs) to promoters. Whereas the role of activators in recruiting chromatin remodeling activities has been clearly demonstrated, the contributions of the transcription machinery have not been firmly established. Here we demonstrate that the remodeling of the RNR3 promoter requires a number of GTFs, mediator and RNA polymerase II. We also show that remodeling is dependent upon the SWI/SNF complex, and that TFIID and RNA polymerase II are required for its recruitment to the promoter. In contrast, Gcn5p-dependent histone acetylation occurs independently of TFIID and RNA polymerase II function, and we provide evidence that acetylation increases the extent of nucleosome remodeling, but is not required for SWI/SNF recruitment. Thus, the general transcription machinery can contribute to nucleosome remodeling by mediating the association of SWI/SNF with promoters, thereby revealing a novel pathway for the recruitment of chromatin remodeling activities.[Keywords: Chromatin remodeling; SWI/SNF; TAFs; RNR3; SAGA; TFIID] Supplemental material is available at http://www.genesdev.org.

SummaryThe Male-specific lethal (MSL) complex up-regulates the single male X chromosome to achieve dosage compensation in Drosophila. We have proposed that MSL recognition of specific entry sites on the X is followed by local targeting of active genes marked by H3K36 trimethylation. Here we analyze the role of the MSL3 chromodomain in the second targeting step. Using ChIP-chip analysis, we find that MSL3 chromodomain mutants retain binding to chromatin entry sites, but show a clear disruption in the full pattern of MSL targeting in vivo, consistent with a loss of spreading. Furthermore, when compared to wild-type, chromodomain mutants lack preferential affinity for nucleosomes containing H3K36me3 in vitro. Our results support a model in which activating complexes, like their silencing counterparts, use the nucleosomal binding specificity of their respective chromodomains to spread from initiation sites to flanking chromatin.