Analysis of a BrdU-sensitive site in the cactus mouse (Peromyscus eremicus): chromosomal breakage and sister-chromatid exchange.

When the thymidine analog BrdU was incorporated into the DNA of a fibroblast cell line derived from the cactus mouse Peromyscus eremicus, a chromosome region with an increased frequency of gaps and breaks was observed. Nearly a third of the chromatid aberrations found at this site were associated with a sister-chromatid exchange (SCE) although this chromosome region showed no increase in sister-chromatid exchange in the absence of a gap or break. SCEs were significantly decreased in the remainder of the chromosome arm when it contained an aberration at the unstable site. This BrdU-sensitive region, unlike others reported, was found not to be late-replicating.--In this chromosome complement, the frequency of sister-chromatid exchange in C-band positive regions was significantly lower than that in C-band negative regions.