Haematophagous insects are frequently carriers of parasitic diseases, including malaria. The mosquito Anopheles gambiae is the major vector of malaria in sub-Saharan Africa and is thus responsible for thousands of deaths daily. Although the role of olfaction in A. gambiae host detection has been demonstrated, little is known about the combinations of ligands and odorant binding proteins (OBPs) that can produce specific odor-related responses in vivo. We identified a ligand, indole, for an A. gambiae odorant binding protein, AgamOBP1, modeled the interaction in silico and confirmed the interaction using biochemical assays. RNAi-mediated gene silencing coupled with electrophysiological analyses confirmed that AgamOBP1 binds indole in A. gambiae and that the antennal receptor cells do not respond to indole in the absence of AgamOBP1. This case represents the first documented instance of a specific A. gambiae OBP–ligand pairing combination, demonstrates the significance of OBPs in odor recognition, and can be expanded to the identification of other ligands for OBPs of Anopheles and other medically important insects.

Elevation of the incubation temperature of Chinook salmon embryo cells from 20 to 24 degrees C or exposure to heavy metals such as CdCl2 (5 microM) or ZnCl2 (100 to 500 microM) induces the reversible expression of a set of heat shock or stress proteins. Continuous exposure of the cells to either metal ions or heat shock results in recovery of protein synthesis to a control-like pattern. Treatment of these cells with either ZnCl2 or CdCl2 also induces the protein metallothionein. Heat shock, however, does not induce metallothionein, suggesting that it does not belong to the common group of heat shock or stress proteins. The induction of these stress proteins can be inhibited by pretreatment with actinomycin D, suggesting that their expression is regulated at the transcriptional level. The major stress proteins are detectable in the products of an in vitro translation system programmed with RNA isolated from heat shock- or metal ion-treated cells. A recombinant DNA probe complementary to Drosophila mRNA coding for the 70,000-dalton heat shock protein was found to hybridize to RNA isolated from heat shock-or metal ion-treated cells but not from control cells. The fish mRNA coding for the heat shock protein with a molecular weight of 70,000 appears to be of similar size to the corresponding Drosophila mRNA.