DOSAGE COMPENSATION IN DROSOPHILA - THE X-CHROMOSOMAL BINDING OF MSL-1 AND MLE IS DEPENDENT ON SXL ACTIVITY

In Drosophila, dosage compensation, i.e. the equalization of levels of X-linked gene products in the two sexes, is achieved by the hypertran scription of most X-linked genes in males relative to females. The pro ducts of at least four genes, collectively termed male-specific lethal (msl) genes, are required for this process and, at least in the case of three of them, mediate this function through an association with th e X chromosome in males. We have studied some of the parameters that a ffect the association of the msl-1 gene product and found that its pre sence is dependent on the wildtype function of the other three genes, leading to the conclusion that these gene products contribute to the f ormation of a multi-subunit complex. Furthermore, the X-chromosomal as sociation of the msl-1 and mle gene products is negatively correlated with the level of function of the master regulatory gene Sxl and can a ssume either a mosaic or a uniform distribution in the tissues of muta nt XX individuals. Surprisingly, we also found that the association of these two msl gene products with the two X chromosomes in females of certain mutant genotypes does not result in the hypertranscription of X-linked genes or in any apparent reduction in viability.