Genetic studies of membrane excitability in Drosophila: lethal interaction between two temperature-sensitive paralytic mutations.

Two mutants of Drosophila melanogaster, parats1 (1-53.9) and napts (2-56.2) both display similar temperature-sensitive paralysis associated with blockage in the conduction of nerve action potentials, suggesting that the two gene products have a similar function. This idea is supported by the observation that the double mutant is unconditionally lethal. Genetic analysis of this synergistic interaction has revealed the following: it specifically involves the para and nap loci; all para alleles interact with napts, but the strength of the interaction varies in an allele-dependent fashion; lethality of the double mutant occurs during the first larval instar with parats1 but differs with other para alleles; hypodosage of para+ causes lethality in a napts background. These results together with previous electrophysiological, behavioral and pharmacological studies of these mutants suggest that both para and nap affect sodium channels and possibly encode different subunits.