DNA Replication and Post-replication Repair in U.V.-sensitive Mouse Neuroblastoma Cells

Abstract

Mouse neuroblastoma cells differentiate when grown in the absence of serum. Differentiation is reversed on the addition of serum. Differentiated cells are more sensitive to UV radiation than proliferating cells. Whereas addition of serum to differentiated neuroblastoma cells normally results in immediate, synchronous entry into the S phase, irradiation just before the addition of serum results in a long delay in the onset of DNA replication. During this lag period, incorporated 3H-thymidine appears in the light density region of CsCl gradients, reflecting repair synthesis or abortive replication. Postreplication repair (gap filling) was present in proliferating cells and at certain times in differentiated cells. The sensitivity of differentiated neuroblastoma cells to UV radiation may be due to ineffective postreplication repair or deficiencies in more than 1 repair mechanism, with reduction in repair capacity beyond a critical threshold.