Alteration of potassium channel gating: molecular analysis of the Drosophila Sh5 mutation.

The Drosophila Shaker (Sh) gene encodes a family of voltage-gated K+ channels. Mutant alleles of Sh alter the currents expressed from these channels in a variety of ways. To identify the molecular basis of these alterations, Sh transcript sequences were amplified using the polymerase chain reaction after reverse transcription of mutant RNA. Amplified products from each mutant were cloned and sequenced. Two alleles, Sh102 and Sh5, had single base substitutions in the central conserved region shared by all Sh channels. RNA synthesized in vitro from a cDNA construct carrying the Sh5 mutation was injected into Xenopus oocytes. Currents expressed by the mutant RNA were altered in their voltage dependence of activation and inactivation, similar to the alterations in Sh currents recorded from different preparations of Sh5 fly tissue. The changes in current properties and the location of the mutation are consistent with the participation of a novel region of the channel in voltage gating.