Molecular and General Genetics MGG

, Volume 161, Issue 3, pp 297–304 | Cite as

A possible model for the structure of the Neurospora carbamoyl phosphate synthase-aspartate carbamoyl transferase complex enzyme

  • A. J. Makoff
  • F. P. Buxton
  • A. Radford


The pyrimidine-3 locus of Neurospora crassa specifies a multienzyme complex comprising pyrimidine-specific carbamoyl phosphate synthase (CPSpyr) and aspartate carbamoyl transferase (ACT). It appears to be divided into a translationally proximal CPS-specific region and a distal ACT-specific region.

Levels of complementation for ACT activity between pairs of four pyr-3 CPS+ACT- mutants showed a range from 12% to 68% of the wild-type level of the enzyme. This is interpreted as interallelic complementation, contradicting certain earlier suggestions of two dissimilar ACT subunits.

Proteolysis of an extract from a heterokaryon formed from two of the above CPS+ACT- alleles (α and β) did not lead to loss of ACT activity, but led to the formation of a fragment with ACT activity with a similar molecular weight (92,000 daltons) to that produced in extracts of wild type strain.

The pyr-3 polar mutant 43–174, which is enzymatically CPS+ACT- and which fails to complement with any other CPS+ACT- alleles, thus suggesting its location towards the proximal end of the ACT region, has CPS activity associated with a form of 180,000 daltons molecular weight. These findings are used to construct a model for the structure of the native enzyme complex.


Enzyme Wild Type Strain Native Enzyme Neurospora Crassa Carbamoyl 
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Copyright information

© Springer-Verlag 1978

Authors and Affiliations

  • A. J. Makoff
    • 1
  • F. P. Buxton
    • 1
  • A. Radford
    • 1
  1. 1.Department of GeneticsThe University of LeedsLeedsU.K.

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