CLONING AND SEQUENCING OF THE PARA-TYPE SODIUM-CHANNEL GENE FROM SUSCEPTIBLE AND KDR-RESISTANT GERMAN COCKROACHES (BLATTELLA-GERMANICA) ANDHOUSE-FLY (MUSCA-DOMESTICA)

Using reverse transcription polymerase chain reactions (RT-PCR), the D NA sequence for the main membrane-spanning region (IS3 through IVS6) o f the gene encoding the alpha-subunit of the para sodium channel of th e German cockroach, Blattella germanica, has been determined. The over all structure of the open reading frame region of this B. germanica ge ne is very similar to that of the par a gene of Drosophila melanogaste r, and that of the partially sequenced par a gene of Musca domestica. On the other hand, it is distinctly different from that of the DSC gen e (Drosophila sodium channel). As a result of a side-by-side compariso n of the pal a gene sequences of the susceptible CSMA strain and the k dr resistant VT strain of B. germanica, one mutation (TTG to TTC) at t he approximate center of the IIS6 membrane-spanning segment was found to result in an amino acid change from L to F. While the functional me aning of this mutation for the operation of the para sodium channel re mains to be studied, this region is very highly conserved among all so dium channels identified so far, and is one of the most hydrophobic ar eas of the entire alpha-subunit. For comparison, we have studied the s ame reg ion of the para sodium channel of both kdr and susceptible SBO strain of the housefly, Musca domestica. We found the homologous type of mutation, CTT to TTT, resulting in the same amino acid alteration (L to F) at this site. However, in the case of houseflies both kdr and susceptible strains contained both L and F versions of the protein. T he ratio of TTT to CTT was significantly higher in the kdr strain of M . domestica than in the three susceptible strains examined.