Mechanism of resistance of Cladosporium cucumerinum against 6-azauracil and 6-azauridinemonophosphate

The mechanism of resistance of strain R of Cladosporium cucumerinum resistant to 6-azauracil (AzU), 6-azauridine (AzUR) and to 6-azauridinemonophosphate (AzUMP) has been studied. Conversion of AzU into AzUR proceeds in the wild strain N and the resistant strain N equally well. Both, strain N and strain R convert AzUR into AzUMP. However, the amount of AzUMP detected in the resistant strain was approximately, three times lower than in strain N. This may be due to a change in the enzyme uridine kinase. The poor ability to form AzUMP from AzUR resulted in a higher activity of the enzyme orotidine monophosphate decarboxylase (OMP-decarboxylase) in strain R in this way interfering less with the incorporation of orotic acid into RNA of strain R than in that of strain N.