The XIST RNA chromatin complex is triggering other mechanisms for inactivating the X-chromosome. Various promoters are methylated and the chromatin structure becomes condensed via histone modifications like methylation and deactylation. This nucleosome changes are leading then to the formation of heterochromatin occuring as Barr bodies (A) Attributes of the inactive x chromosome XIST RNA Production XIST/Barr body complex Histone H4 hypoacetylation Histone H3 methylation Histone macroH2AI concentration Nuclear envelope association Late replication Heterochromatin Methylated promoters Figure 5.24 The inactive x chromosome of human female cells contains underacetylated histone H4.(A) Mouse XIST RNA( red)on an Chromosomes from a human female fibroblast ell stained green with fluorescent antibody to inactive X-chromosome( blue) acetylated histone H4. while all the other chro- mosomes are stained green, the inactive X is not and thus appears red (arrow). (B)List of On the active x-chromosome attributes characterizing the inactive X chro- mosome (From Jeppesen and Turner 1993; the promoter for XIST is photograph courtesy of the authors. methylated and so inactiveMouse XIST RNA ( red ) on an inactive X-chromosome ( blue) . On the active X-chromosome the promoter for XIST is methylated and so inactive The XIST RNA chromatin complex is triggering other mechanisms for inactivating the X-chromosome . Various promoters are methylated and the chromatin structure becomes condensed via histone modifications like methylation and deactylation . This nucleosome changes are leading then to the formation of heterochromatin occuring as Barr bodies