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Some Properties of a DNA-unwinding Protein Unique to Lymphocytes from Chronic Lymphocytic Leukemia¹

Division of Hematology and Oncology, Department of Medicine, Duke University Medical Center and Durham Veterans Administration Hospital, Durham, North Carolina 27710

Lymphocytes from a common human leukemia, chronic lymphocytic leukemia, have a greatly enhanced capability of DNA repair and a concomitantly prolonged survival in vitro after damage to DNA. From these lymphocytes, we isolated and purified a DNA-binding protein with a molecular weight of 24,000. It binds tightly to both ultraviolet light (UV)-irradiated and single-stranded DNA. At 35° it enhances the helix-coil transition of poly[d(A-T)] and the UV-irradiated calf thymus DNA but is inefficient in ordinary native DNA. This protein also facilitates the rate of UV-endonuclease incision of UV DNA but does not induce any nicks by itself. This finding suggests that the protein may be involved in DNA repair by enhancing such activity, and also offers an explanation for our observation of increased DNA repair in chronic lymphocytic leukemia cells. When human metaphase chromosomes are exposed to the protein, it induces marked lengthening of chromatids suggesting that this protein may also act on complex chromosomes.

By quantitative immunochemical determinations, such protein could not be found in lymphocyte extracts of three normal individuals.

¹ Research was supported by VA Research Grant 4700-02 and grants from North Carolina Community Health Services

² To whom reprint requests should be addressed, at Box 3835, Duke University Medical Center, Durham, N. C. 27710.

³ USPHS Hematology and Oncology trainee, supported by Grant 5T01CA05042.

Received 10/17/74. Accepted 1/ 7/75.