Summary
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.
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Downey, R., Wiehl, P. A convener role for the cnxH gene specified component in the NADPH-nitrate reductase from Aspergillus nidulans . Mol Cell Biochem 59, 155–163 (1984). https://doi.org/10.1007/BF00231311
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DOI: https://doi.org/10.1007/BF00231311