Nitrogen metabolite repression of fluoropyrimidine resistance and pyrimidine uptake in Neurospora crassa.

Wild type Neurospora crassa was shown to be more resistant to 5-fluoro-uracil, 5-fluoro-uridine and 5-fluoro-2'-deoxyuridine in the presence of ammonia than in its absence. This differential resistance may in part be accounted for by the observation that both uracil and uridine uptake in germinating conidia is under nitrogen metabolite regulation. The uptake of uracil and uridine is increased on poor nitrogen sources in wild type, is unaffected by nitrogen source in a nit-2 mutant strain while a gln-1 mutant strain showed intermediate behaviour. Wild type also showed increased resistance to all three fluoropyrimidines with increased temperature and both uracil and uptake in the wild type increased with temperature and both uracil and uridine uptake in the wild type increased with temperature.