NAPTS, A MUTATION AFFECTING SODIUM-CHANNEL ACTIVITY IN DROSOPHILA, IS AN ALLELE OF MLE, A REGULATOR OF X-CHROMOSOME TRANSCRIPTION

nap(ts) is a recessive mutation that affects the level of sodium channel activity and, at high temperature, causes paralysis associated with a loss of action potentials. We show, by genetic complementation tests, germline transformation, and analysis of mutations, that nap(ts) is a gain-of-function mutation of mle, a gene required for X chromosome dosage compensation and male viability. Molecular analyses of nap and mle mutations indicate that mle+, nap+, and nap(ts) activities are encoded by the same open reading frame and suggest that nap(ts) is due to a single amino acid substitution. Although nap(ts) is known to act via para+, an X-linked sodium channel structural gene, its effect is not due to a simple defect in para+ dosage compensation.