CLONING AND ANALYSIS OF THE ESTERASE GENES CONFERRING INSECTICIDE RESISTANCE IN THE PEACH-POTATO APHID, MYZUS-PERSICAE (SULZER)

Full-length cDNA clones encoding the esterases (E4 and FE4) that confe r insecticide resistance in the peach-potato aphid [Myzus persicae (Su lzer)] were isolated and characterized. The E4 cDNA contained an open reading frame of 1656 nucleotides, coding for a protein of 552 amino a cids. The FE4 cDNA shared 99% identity with E4 over this region, the m ost important difference being a single nucleotide substitution result ing in the FE4 mRNA having an extra 36 nucleotides at the 3' end. The derived amino acid sequences for the N-terminus of E4 and FE4 were ide ntical, with the first 23 residues being characteristic of a signal pe ptide and the next 40 residues being an exact match to the N-terminal sequence determined by Edman degradation of both purified proteins. Th e predicted molecular masses of 58.8 and 60.2 kDa for the E4 and FE4 p olypeptides were consistent with those previously observed by in vitro translation of mRNA. Five potential N-linked glycosylation sites were present in both polypeptides, in accordance with earlier evidence tha t the native esterases are glycoproteins. Comparison of the aphid este rase protein sequences with other serine hydrolases provided evidence that their activity involves a charge-relay system with a catalytic tr iad the same as that found in acetylcholinesterase. Restriction mappin g and sequencing of cloned genomic DNA showed that the E4 gene is spre ad over 4.3 kb with six introns and that the previously reported diffe rences between the 3' ends of the E4 and FE4 genes result from single nucleotide substitutions and not gross differences in the DNA sequence s.