Late induction of <i>roX1</i> expression requires <i>roX2</i> RNA.

<p>In nuclei where dosage compensation was successfully turned on after late <i>msl2</i> induction, extensive <i>roX2</i> was observed painting the entire X chromosome. (A) However, only 1% of the chromosomes showed extensive <i>roX1</i> painting. 34% and 59% of chromosomes showed <i>roX1</i> expression confined to several Mbp around (B) or just at the endogenous <i>roX1</i> locus (C), respectively. The remaining chromosomes (6%) had no <i>roX1</i> expression despite the presence of <i>roX2</i> (data not shown). <i>roX1</i> and <i>roX2</i> were detected by biotin (green, A–C) and digoxigenin (red, A′–C′) labeled antisense riboprobes, respectively. The merged figure is shown in A″–C″. White arrows denote the endogenous <i>roX1</i> locus at band 3F.