Tracer studies of pyrimidine synthesis by Neurospora crassa 1298.

Previous reports from thii laboratory have described the growth-supporting abilities of a-aminobutyric acid, propionic acid, and certain related compounds for the pyrimidmelessstrain, Neurospora crassu 1298 (1, 2). Tracer studies with aminobutyric acid-3-Cl4 indicated the use of this compound by the mold as a precursor of the pyrimidines of the ribonucleic acids (3). This conclusion, however, was subject to some doubt in that considerable dilution of the radioactive carbon was found to have occurred during pyrimidine formation. The present report provides evidence confirming the role of aminobutyrate as a relatively specific pyrimidine precursor in this organism and extending this conclusion to propionate as well. Studies of the use of uracil-2-C” for ribonucleic acid pyrimidine production under various conditions are also described.