Replication pattern and quinacrine fluorescence of the chromosomes of a CV-1-derived african green monkey cell line

When tritiated thymidine is incorporated into cells of a heteroploid CV-1-derived line near the end of the DNA synthetic period (S). the chromosomes are preferentially labeled in the centromeric region. After staining with quinacrine, the centromeric region of every chromosome shows minimal fluorescence, whereas the remainder of most chromosomes shows fairly bright fluorescence with distinctive banding patterns. In contrast to the end-of-S pattern, the distribution of grains over chromosomes labeled during the middle of S is consistent with random labeling. A marker chromosome with a long secondary constriction in the long arm near the centromere possesses the same labeling pattern, with late replication limited to the centromeric region and perhaps the adjacent region of the short arm. The secondary constriction region itself is not late replicating, and it fails to fluoresce after quinacrine staining.