Guild by association - non-coding RNAs, chromosome-specific proteins and dosage compensation in Drosophila

Dosage compensation is a striking example of the interplay between gene-spe cific regulation and chromosomal architecture. This process has evolved to make X-linked gene expression equivalent in males with one X chromosome and females with two. Examining species at the molecular level has shown that dosage compensation is mediated by sex-specific factors that decorate the X chromosomes to regulate chromatin structure and gene expression. In Drosop hila, dosage compensation is achieved, at least in part, through site-speci fic histone H4 acetylation, which is modulated by a male- and X-specific pr otein complex. The discovery of non-coding RNAs that 'paint' dosage-compens ated X chromosomes in mammals and in Drosophila suggests that RNAs play an intriguing, unexpected role in the regulation of chromatin structure and ge ne expression.