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Influence of Thymine Starvation on the Integrity of Deoxyribonucleic Acid in Escherichia coli

Department of Biology, The University of Texas M. D. Anderson Hospital and Tumor Institute, Houston, Texas 77025

ABSTRACT

The influence of thymine starvation on the single-strand molecular weight of deoxyribonucleic acid (DNA) from Escherichia coli was determined by sedimentation through gradients of alkaline sucrose. Growth of cells for as long as 150 min in thymineless medium did not significantly reduce the molecular weight below the control value of 2.4 ± 0.3 x 10⁸ daltons. Incubation of cells in thymineless medium after exposure to 500 ergs/mm² of ultraviolet light or 20 krad of ¹³⁷Cs gamma rays did not appear to block the rejoining of single-strand breaks associated with irradiation. Thus, DNA repair enzymes, presumably including DNA ligase, are not significantly inhibited by thymine starvation.