The L5178Y S/S Murine Leukemic Lymphoblast: A Radiosensitive, Malignant Cell of Stable Karyotype

stable chromosomal complement with a modal chromosome number of 40 (2n = 40). The only variation from the G-banded wild-type karyotype of the mouse is a Y-chromosome deletion. Since the malignant cell line has been established for 16 years and is sensitive to X rays, the stability of the karyotype provides the essential property needed for utilizing the cell in investigations of the genetic control of cellular (DNA) repair. One unique response of the cell to X rays is a single peak of radioresistance at, or very near, the S-G2 border. Through [3H]TdR autoradiography, we have found that chromosomes 14 and 15 replicate significantly more than other chromosomes at that time, while they label little during early S.