Drosophila male-specific lethal 2 protein controls sex-specific expression of the roX genes

The MSL complex of Drosophila upregulates transcription of the male X chromosome, equalizing male and female X-linked gene expression. Five male-specific lethal proteins and at least one of the two noncoding roX RNAs are essential for this process. The roXRNAs are required for the localization of MSL complexes to the X chromosome. Although the mechanisms directing targeting remain speculative , the ratio of MSL protein to roX RNA influences localization of the complex. We examine the transcriptional regulation of the roX genes and show that MSL2 controls inale-specific roX expression in the absence of any other MSL protein. We propose that this mechanism maintains a stable MSL/ roX ratio that is favorable for localization of the complex to the X chromosome.