Forward and back mutation in thepyr3region of Neurospora. I. Mutations from arginine dependence to prototrophy

A system for the screening of reversions in an arginine-dependent strain of Neurospora has been developed. Reversion resulted from any one of three events: (a) Back mutation of the originalarggene. (b) Forward mutation at thepyrlocus. This has the pleiotropic effect of suppressingargwhile determining a pyrimidine requirement. Interaction with the unmutated nuclei of the same conidium permits growth on minimal medium. (c) Forward mutation at thepyrlocus to alleles of intermediate activity. These alleles suppressarg, but do not create a pyrimidine requirement.