Probing sister chromatid exchange formation with halogenated pyrimidines

This communication describes the use of 6 different halogenated pyrimidine analogues, bromodeoxyuridine (BrdUrd), chlorodeoxyuridine (CldUrd), iododeoxyuridine (IdUrd), bromodeoxycytidine (BrdCyd), chlorodeoxycytidine (CldCyd), and iododeoxycytidine (IdCyd), to achieve sister chromatid differentiation (SCD) and evaluate sister chromatid exchange (SCE) formation in mitogen-stimulated human lymphocytes. Also included are a description of an in vivo experiment with BrdUrd, CldUrd, and IdUrd; a discussion of pyrimidine metabolism effects on SCEs; and the presentation of an update on the "conformation hypothesis" for SCE formation. This hypothesis revision includes a model that centers on the idea that the sum of the conformational alterations of the DNA polymerase-DNA template complex at replication is the controlling factor in SCE formation.