Translational control of dosage compensation in Drosophila by sex-lethal: cooperative silencing via the 5 ' and 3 ' UTRs of msl-2 mRNA is independentof the poly(A) tail

Translational repression of male-specific-lethal 2 (msl-2) mRNA by Sex-leth al (SXL) controls dosage compensation in Drosophila. Irt vivo regulation in volves cooperativity between SXL-binding sites in the 5' and 3' untranslate d regions (UTRs). To investigate the mechanism of msl-2 translational contr ol, we have developed a novel cell-free translation system from Drosophila embryos that recapitulates the critical features of mRNA translation in euk aryotes: cap and poly(A) tail dependence. Importantly, tight regulation of msl-2 translation in this system requires cooperation between the SXL-bindi ng sites in both the 5' and 3' UTRs, as seen lit vivo. However, in contrast to numerous other developmentally regulated mRNAs, the regulation of msl-2 mRNA occurs by a poly(A) tail-independent mechanism. The approach describe d here allows mechanistic analysis of translational control in early Drosop hila development and has revealed insights into the regulation of dosage co mpensation by SXL.