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

Institute of Radiation Biology, University of Tennessee, Knoxville, Tennessee 37916
Biology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830

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 [5-³H]-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 x 10³ counts per min per µg. The DNA was isolated by elution from hydroxyapatite columns with sodium phosphate buffer (0.40 M, pH 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.