Xist RNA exhibits a banded localization on the inactive X chromosome and is excluded from autosomal material in cis.

The propagation of X chromosome inactivation is thought to be mediated by the cis- limited spreading of the non-protein coding Xist transcript. In this report we have investigated the localization of Xist RNA on rodent metaphase chromosomes. We show that Xist RNA exhibits a banded pattern on the inactive X and is excluded from regions of constitutive heterochromatin. The banding pattern suggests a preferential association with gene-rich, G-light regions. Analysis of X:autosome rearrangements revealed that restricted propagation of X inactivation into cis -linked autosomal material is reflected by a corresponding limited spread of Xist RNA. We discuss these results in the context of models for the function of Xist RNA in the propagation of X inactivation.