Isoorotate decarboxylase activity present in various strains of Neurospora /

Abstract

N. crassa is known to utilize a salvage pathway for the production of uracil. This is known as the pyrimidine salvage pathway. This pathway consists of four enzymatic steps to convert thymidine to uracil. The final enzyme is isoorotate decarboxylase (lDCase), which forms uracil from isoorotate through a decarboxylation reaction. An in vitro assay for IDCase activity has been developed, which allowed the determination of specific activity of the enzyme in various strains of Neurospora. We attempted first to determine if another species ofNeurospora contained this pathway by looking for the presence of the IDCase enzyme. N. africana was chose because it is a homothallic, aconidiate species unlike N. crassa which is heterothallic and conidiated. We were able to determine that N. africana did contain this enzyme and with higher activity than in N. crassa. We next obtained the FGSC# 2203 triple mutant Ctm::.1, uc-l, uc-2) to begin to look at the effect of the mutations on the activity of the IDCase enzyme. We concluded that the I2Y!:1 mutation has little to no effect on the activity of IDCase based on the fact that a I2Y!:1 transformant that retained the two uc mutations had relatively the same amount of IDCase activity as the triple mutant.