Differential spiralization along mammalian mitotic chromosomes

The morphology of human metaphase chromosomes of peripheral blood lymphocytes taken from normal persons of both sexes and cultured at the final stages of the S-period in the presence of 5-bromodeoxyuridine (BUdR), or 5-bromodeoxycytidine (BCdR) was studied. It was observed that the chromosomes of the complement were capable of responsing to the treatment with analogs by the appearance of extended segments along their length. The pattern of segmentation was constant and specific for a given chromosome, serving as a basis for its identification, and appeared to be similar for both analogs. — Autoradiography of such chromosomes performed with ³H-thymidine (³H-TdR), ³H-deoxycytidine (³H-CdR), and ³H-BUdR showed that the extended chromosomal segments are late replicating. In accordance with this correlation, the most regular and distinctive segmentation was observed in chromosomes having large late replicating regions, such as Nos. 4, 6, 9, 13, 16, X, and Y. — A comparative analysis of the BUdR-induced differential spiralization pattern and banding pattern obtained with the G-staining technique was carried out. A good correspondence between the extended segments and Giemsa-positive bands was found. The data are discussed in relation to the mechanism of differential staining of metaphase chromosomes.