DPY-27 - A CHROMOSOME CONDENSATION PROTEIN HOMOLOG THAT REGULATES C. ELEGANS DOSAGE COMPENSATION THROUGH ASSOCIATION WITH THE X-CHROMOSOME

dpy-27 is an essential dosage compensation gene that acts to reduce ex pression of both hermaphrodite X chromosomes. The DPY-27 protein becom es specifically localized to the X chromosomes of wild-type XX embryos , but remains diffusely distributed throughout the nuclei of male (XO) embryos. In xol-1 mutant XO embryos that activate the XX mode of dosa ge compensation and die from inappropriately low X chromosome transcri pt levels, DPY-27 becomes localized to X. Therefore, sex specificity o f the dosage compensation process is regulated at the step of DPY-27 X chromosome localization. DPY-27 exhibits striking similarity to prote ins required for assembly and structural maintenance of Xenopus chromo somes in vitro and for segregation of yeast chromosomes in vivo. These findings suggest a link between global regulation of gene expression and higher order chromosome structure. We propose that DPY-27 implemen ts dosage compensation by condensing the chromatin structure of X in a manner that causes general reduction of X chromosome expression.