JIL-1 and Transcriptionn Figure 7. Distribution of JIL-1 on the X-chromosome. (A) Localization of JIL-1 (left panels, green in the merged pictures) in SXB1-2C and 2xNOPU females expressing increasing amounts of MSL2 (coloured red in the merged pictures on the right). (B) Densities of various features on active X-chromosomal genes grouped by increasing distance from high affinity sites (HAS) for the DCC. There are 115, 121, 405 and 465 genes in the group of genes located at increasing distances from HAS, respectively. doi:10.1371/journal.pgen.1001327.g007 and H4K16ac, on the X-chromosome suggesting that JIL-1 recruitment occurs downstream of those two histone marks. Interestingly, the correlation still holds for autosomal probes, although autosomal H4K16ac is at least in part placed at the 59 end of genes by alternative MOF complexes [26,46,47]. JIL-1 recruitment has also been linked to the H4K12ac mark, which is placed by the GCN5-containing ATAC complex [48]. However, Workman and colleagues recently found that ATAC also contains an acetyltransferase with specificity for H4K16 (atac2), which may contribute to JIL-1 recruitment [49]. In the cases of very strong transcription activation by high levels of Gal4 activator, we did not see an accumulation of JIL-1 to endogenous levels. Conversely, JIL-1 is also not enriched at developmental puffs on polytene chromosomes where robust transcription takes place according to the strong ePol staining (Figure S1). The massive heat-induced activation leads to extensive chromatin decondensation (puffing) on polytene chromosomes, which is probably accompanied by nucleosome loss [41]. In summary, we favour the idea that the recruitment of JIL-1 relies on several, partly redundant features of active chromatin. JIL-1 harbours an H3-tail binding domain in its C-terminus and another determinant of chromatin targeting in its N-terminal domain [3], but it does not contain any domain known to directly bind modified histone tails. Its recruitment to active chromatin is, therefore, most probably indirect. We know of no histone modification or any other chromatin-associated feature to be enriched on the male X PLoS Genetics | www.plosgenetics.org 11 March 2011 | Volume 7 | Issue 3 | e1001327