Isolation and characterisation of a cytochrome b5 cDNA clone from Helicoverpa armigera (Hubner): possible involvement of cytochrome b5 in cytochrome P450 CYP6B7 activity towards pyrethroids

A cDNA clone specific for cytochrome b5 was isolated from Helicoverpa armig era. This sequence corresponded to a mRNA of an estimated 544 nucleotides i n length excluding the poly A tail. The mRNA contained an open reading fram e of 381 nucleotides encoding a protein of 127 amino acid residues with a m olecular weight of 14,564 Daltons. The encoded protein sequence showed 51% protein sequence identity with cytochrome b5 from M. domestica and 36-37% i dentity with mammalian and avian cytochrome b5 sequences. Northern analysis of larval RNA using this cDNA as probe, revealed that cytochrome b5 mRNA e xpression is tissue specific with the mRNAs being expressed in abundance in the midguts of larvae, at a lower level in fatbody but is not detectable i n larval integument. During normal development this mRNA was undetectable i n eggs but was present at similar levels from first to fifth instar larvae. The mRNA was expressed at very low levels in pupae and adult moths. The cy tochrome b5 mRNA was found to be inducible by treatment with the monoterpen e, a-pinene, and to be over-expressed in some individuals of a pyrethroid r esistant population of H. armigera. The induction and over-expression patte rns were identical to the cytochrome P450, CYP6B7 mRNA. The present data su ggests that cytochrome b5 may be involved in CYP6B7 mediated pyrethroid res istance in H. armigera. (C) 1999 Elsevier Science Ltd. All rights reserved.