Characterization of qa-2 mutants of Neurospora crassa by genetic, enzymatic, and immunological techniques
Genetic and complementation mapping studies using 20 qa-2 mutants defective for catabolic dehydroquinase indicate that the qa-2 gene encodes a single polypeptide chain and is the structural gene for catabolic dehydroquinase, a 220,000-molecular-weight protein composed of identical 10,000-molecular-weight subunits. Many qa-2 mutants are capable of reversion, but no evidence has yet been obtained for nonsense mutations in this gene. The biochemical consequences of the mutations in two complementing qa-2 strains (M239 and M204) have been determined. Both mutants have extremely low levels of catalytic activity and form a heterocaryon with about 4 percent of the wild-type activity. As assayed by immunological cross-reactivity, mutant M239 and the heterocaryon have nearly wild-type levels of native-molecular-weight catabolic dehydroquinase protein, whereas M204 has no detectable amount of this protein. Thus it is concluded that M239 has a mutation at or near the catalytic site which reduces the activity 10,000-fold but has little or no influence on the formation of the native multimeric structure. In contrast, M204 apparently has a mutation that severely inhibits aggregation and may have only a minor effect on the inherent potential for catalytic conversion at the reactive site. The heterocaryon would appear to form a mixed multimer with the monomeric subunits from M239 providing the aggregated structure and those from M204, the catalytically active moiety.
- Research Organization:
- Univ. of Georgia, Athens
- OSTI ID:
- 7100333
- Journal Information:
- J. Bacteriol.; (United States), Vol. 129:1
- Country of Publication:
- United States
- Language:
- English
Similar Records
Coordinate activation of a multienzyme complex by the first substrate. Evidence for a novel regulatory mechanism in the polyaromatic pathway of Neurospora crassa
Activator-independent gene expression in Neurospora crassa