THE NTPASE HELICASE ACTIVITIES OF DROSOPHILA MALELESS, AN ESSENTIAL FACTOR IN DOSAGE COMPENSATION/

Drosophila maleless (mle) is required for X chromosome dosage compensa tion and is essential for male viability, Maleless protein (MLE) is hi ghly homologous to human RNA helicase A and the bovine counterpart of RNA helicase A, nuclear helicase II. In this report, we demonstrate th at MLE protein, overexpressed and purified from Sf9 cells infected wit h recombinant baculovirus, possesses RNA/DNA helicase, adenosine triph osphatase (ATPase) and single-stranded (ss) RNA/ssDNA binding activiti es, properties identical to RNA helicase A. Using site-directed mutage nesis, we created a mutant of MLE (mle-GET) that contains a glutamic a cid in place of lysine in the conserved ATP binding site A. In vitro b iochemical analysis showed that this mutation abolished both NTPase an d helicase activities of MLE but affected the ability of MLE to bind t o ssRNA, ssDNA and guanosine triphosphate (GTP) less severely. In vivo , mle-GET protein could still localize to the male X chromosome coinci dentally with the male-specific lethal-1 protein, MSL-1, but failed to complement mle(1) mutant males, These results indicate that the NTPas e/helicase activities are essential functions of MLE for dosage compen sation, perhaps utilized for chromatin remodeling of X-linked genes.