UNCONVENTIONAL ORGANIZATION OF AMPLIFIED ESTERASE-B GENE IN INSECTICIDE-RESISTANT MOSQUITOS OF THE CULEX-PIPIENS COMPLEX

The amplified esterase B gene responsible for resistance to organophos phorus insecticides in Culex mosquitoes is shown to form a DNA ''puff' ' in salivary gland polytene chromosomes. This ''puff'' is absent in s usceptible mosquitoes lacking the amplified gene, and unlike all puffs known today, it is neither related to development nor involved in pro tein synthesis. The ''puff'' therefore corresponds to a special arrang ement of the very large number of copies (possibly up to 250,000) of t he 25-30-kb DNA fragment encompassing the esterase B structural gene i n polytene chromosomes. In addition, the amplified and nonamplified es terase B gene(s) were found to be localized on chromosome 2L, and flan ked by identical banding patterns, indicating the absence of an import ant chromosome rearrangement before, during, or after gene amplificati on.