title: A convener role for the cnxH gene specified component in the NADPH-nitrate reductase fron Aspergillus nidulans.
abstract: The role of the cnxH+ gene specified polypeptide in the formation and function of the NADPH-nitrate reductase in Aspergillus nidulans was examined with the use of two complementing mutant strains which were grown as forced heterocaryons in the presence of nitrate. The niaD-421 structural gene mutant and the cnxH-318 co-factor gene mutant produce two components of the NADPH-cytochrome c reductase co-activity which can be distinguished by their enzymatic and physical behavior. This combination enabled us to isolate the de novo synthesis of niaD+ gene specified protomers from the constitutively formed co-factor at two stages of development. The proportion of induced and constitutively formed protomers in the isolated holoenzyme was measured after pulsing with [3H]-histidine or [14C]-histidine prior to induction with nitrate. The newly formed nitrate reductase was resolved by agarose gel electrofocusing and activity staining. In vivo assembly of a 7.8s enzyme in the heterocaryotic mycelium of the above strains is apparently achieved by the convener action of the cnxH+ gene directed polypeptide from the niaD- strain on the niaD+ gene directed protomers of the cnxH- partner. This occurs with or without Mo as a co-factor.
mesh_terms: D001233:Aspergillus nidulans / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D005800:Genes, Fungal; D006639:Histidine / Q000378:metabolism; D007525:Isoelectric Focusing; D008982:Molybdenum / Q000378:metabolism; D009154:Mutation; D009251:NADPH-Ferrihemoprotein Reductase / Q000096:biosynthesis / Q000378:metabolism; D050896:Nitrate Reductase (NAD(P)H); D009565:Nitrate Reductases / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D006639:Histidine; D008982:Molybdenum; D009251:NADPH-Ferrihemoprotein Reductase; D009565:Nitrate Reductases; D050896:Nitrate Reductase (NAD(P)H)