JUVENILE-HORMONE BINDING-COMPONENTS OF LOCUST FAT-BODY

Juvenile hormone (JH) binding components from the fat body of the Afri can migratory locust were analyzed in a search for a potential nuclear JH receptor. Biosynthetically prepared 10R[H-3]JH III gave a high pro portion of specific binding to isolated nuclei and extracted proteins; data obtained with the JH analogs, [H-3]methoprene and [H-3]pyriproxy fen, on the other hand, were obscured by abundant non-specific binding . The vast majority of the high affinity JH III binding activity prese nt in cytosolic and nuclear extracts was due to a high molecular weigh t JH binding protein (JHBP) which has previously been identified in lo cust hemolymph. This protein has several chromatographic forms which i nterfered in the search for a nuclear JH receptor. When specific antis erum was used to remove JHBP from nuclear extracts, a novel IH binding activity (NBP) was detected. NBP could be separated from JHBP by prec ipitation with ammonium sulfate. NBP displayed a high affinity for JH lit (Kd = 0.25 nM) and JH and IH II competed strongly for JH III bindi ng, whereas methoprene and pyriproxyfen showed apparent competition wh en present in 1,000-fold excess. NBP was present in nuclear extracts a t approximately 25,000 sites per cell; levels were similar in male and female locusts and were not greatly affected by the presence or absen ce of JH. The characteristics of NPB make it a strong candidate for a nuclear IH receptor. (C) 1995 Wiley-Liss, Inc.