THE MALE-SPECIFIC LETHAL-ONE (MSL-1) GENE OF DROSOPHILA-MELANOGASTER ENCODES A NOVEL PROTEIN THAT ASSOCIATES WITH THE X-CHROMOSOME IN MALES

male-specific lethal-one (msl-1) is one of four genes that are require d for dosage compensation in Drosophila males. To determine the molecu lar basis of msl-1 regulation of dosage compensation, we have cloned t he gene and characterized its products. The predicted msl-1 protein (M SL-1) has no significant similarity to proteins in the current data ba ses but contains an acidic N terminus characteristic of proteins invol ved in transcription and chromatin modeling. We present evidence that the msl-1 protein is associated with hundreds of sites along the lengt h of the X chromosome in male, but not in female, nuclei. Our findings support the hypothesis that msl-1 plays a direct role in increasing t he level of X-linked gene transcription in male nuclei.