Correction of sister chromatid exchanges in Bloom's syndrome fibroblasts after fusion with cytoplasts from a Chinese hamster cell line.

Cytoplasmic hybrids (cybrids) were prepared by fusion of Bloom's syndrome (BS) fibroblasts with cytoplasts derived from a chloramphenicol (CAP)-resistant cell line of hypoxanthine phosphoribosyl transferase (HPRT)-deficient Chinese hamster wg3h cells to study the role of cytoplasmic and nuclear factors which may involve corrective factor(s) of sister chromatid exchanges (SCEs) of the BS cells. The high rate of SCEs characteristic of the cultured BS fibroblasts was found to be fully corrected in cybrids. This result suggests the existence of a transmissible corrective factor(s) in the cytoplasm of the Chinese hamster cells. Long-term cultures of such cybrids after 3 and 5 weeks of fusion, however, showed a reversion to a high SCE level similar to the parental BS cells, indicating that the corrective factors have not been stable in the cybrid cells.