The location of the feedback-specific region within thePyrimidine-3 locus ofNeurospora crassa

Abstract
Thepyrimidine-3 locus ofNeurospora crassa specifies two enzyme activities, pyrimidine-specific carbamyl phosphate synthetase (CPSpyr) and aspartate transcarbamylase (ATC). ATC is translationally distal. CPSpyr, but not ATC, is subject to feedback inhibition by uridine triphosphate (UTP). To investigate the location of the feedback-specific region within the locus, inhibition of a number ofpyr-3 alleles by UTP was investigated. All CPS+ ATC- polar alleles, revertants of CPS- ATC- polar alleles, and 5-fluorouracil-resistant mutants had normal UTP response. The location of the feedback-specific region is in or close to the CPS-specific region.