Barbara Dyer

Publication Date


Document Type


First Advisor

Frampton, Elon W.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Biological Sciences


Cyanobacteria; Plants; Effect of radiation on; Anacystis nidulans; DNA


An analysis was made of gamma ray-induced single-strand scissions and their subsequent repair in the deoxyribonucleic acid (DNA) of the cyanobacterium (blue-green-alga) Anacystis nidulans. The DNA of exponentially growing cells was labeled with tritiated deoxyadenosine before the cells were irradiated with doses of 20 or 30 kilorads supplied by a ¹³⁷cesium source. Irradiated cells were returned to growth conditions, and samples were removed for analysis on linear5-20% alkaline sucrose gradients a 1 h intervals for a period of 4 h. The sedimentation coefficients (s[sub 20,w]) and molecular weight values of individual fractions from the gradients were calculated by a computer program and indicated that irradiation resulted in a reduction in the size of the single-stranded DNA recovered. Incubation under growth conditions for 1 h resulted in the recovery of larger pieces of DNA, but further incubation resulted in molecules with a reduced average molecular weight. The largest DNA fragment recovered from unirradiated cells had an s[sub 20,w] of approximately 144, yielding a molecular weight value of 3.88 X 10⁸ daltons. Exposure to a 30 kilorad dose produced about 77 single-strand breaks in the genome.


Includes bibliographical references.||Includes illustrations.


vii, 48 pages




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