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Complementation relationships of Neurospora am mutants in relation to their formation of abnormal varieties of glutamate dehydrogenase

Published online by Cambridge University Press:  14 April 2009

J. R. S. Fincham  and
D. R. Stadler
J. R. S. Fincham
Affiliation:
John Innes Institute, Bayfordbury, Hertford, Herts.
D. R. Stadler
Affiliation:
John Innes Institute, Bayfordbury, Hertford, Herts.

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Six new am mutants of Neurospora, am14–am19, with defective formation of NADP-linked glutamate dehydrogenase, were isolated following treatment of conidia with nitrous acid. This brings the number of genetically distinct and viable am mutants to sixteen. Heterocaryon-compatible isolates of each of the new mutants were tested for complementation with each of the mutants previously known. A number of new complementary combinations were found which add to the complexity of the complementation map which, however, remains linear.

The mutants which show complementation are am1, am2, am3, am7, am14 and am19. It has proved possible to isolate an altered form of glutamate dehydrogenase from each of these except am14, which appears to produce no protein fractionating like the normal enzyme. Among the non-complementing mutants, am4 produces an easily-isolated inactive form of glutamate dehydrogenase. These results agree with the immunochemical findings of Roberts & Pateman (1964).

Of the mutationally altered forms of the enzyme, the am1, am2, am3 and am7varieties are electrophoretically identical or closely similar to the normal protein, while the am4 and am19 varieties move faster towards the anode at pH 8·5, am19being the faster of the two. The am19 protein, like the am2 and am3 proteins previously reported on, can be activated to give some enzyme activity, but the activity obtained is much lower for this mutant than for am2 or am3.

All the complementary pairs of mutants, including those involving am19, form active enzyme varieties which have very close to normal electrophoretic properties. In several cases the complementation enzyme is less stable to heat than the wild-type enzyme.

Type
Research Article
Information
Genetics Research , Volume 6 , Issue 1 , February 1965 , pp. 121 - 129
Copyright
Copyright © Cambridge University Press 1965

References

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