Repair of Ultraviolet Light-Induced Damage to the Deoxyribonucleic Acid of Neurospora crassa

Abstract

A method is described for labeling a specific pyrimidine in the deoxyribonucleic acid (DNA) of Neurospora crassa . In cells grown in the presence of [ 5 - 3 H ]-uridine, more than 97% of the radioactivity associated with the DNA had been incorporated into cytosine. The specific activity of the labeled DNA was approximately 3 × 10 3 counts per min per μg. The DNA was isolated by elution from hydroxyapatite columns with sodium phosphate buffer (0.40 m , p H 6.8). This procedure was used to demonstrate that in vegetative cells of N. crassa both photoreactivation and excision repair are operative, as measured by the removal of ultraviolet light-induced cytosine-containing dimers.