An ecdysone-inducible putative "DEAD box" RNA helicase in the spruce budworm (Choristoneura fumiferana).

Abstract RNA helicases are a family of enzymes that unwind nucleic acid duplexes, such as RNA/RNA and RNA/DNA, in a 3′ to 5′ direction into single-stranded polynucleotides. A putative RNA helicase cDNA ( CfrHlc64 ) was isolated from the spruce budworm, Choristoneura fumiferana . CfrHlc64 was 1998 nucleotides in length, and the deduced protein had 565 amino acids with a predicted molecular mass of 64 kDa. It contained eight functional motifs conserved in the “DEAD box” family of RNA helicases. The deduced amino acid sequence showed 10–50% identities to homologues of other species from bacteria to human. In vitro expression of the cDNA resulted in recombinant proteins of 64 kDa as expected from the deduced amino acid sequence. Northern blotting and RT-PCR analyses revealed the presence of CfrHlc64 mRNA in all developmental stages from embryo to adult. Higher levels of CfrHlc64 mRNA were detected in the fat body and midgut than in the epidermis of sixth instar larvae. The CfrHlc64 protein was distributed mainly in the fat body. Female adults expressed CfrHlc64 mRNA at higher levels than male adults. The nonsteroidal ecdysone agonist, tebufenozide, enhanced the expression of CfrHlc64 in a dose-dependent manner.