3h Labeling Patterns of Permanent Cell Line Chromosomes Showing Pulverization or Accentuated Secondary Constrictions

An appearance suggesting extreme fragmentation of chromosomes has been referred to as "pulverization" by Nichols et al. (1). A different appearance, that of accentuated secondary constrictions (or chromomeres), was described by Stubblefield in a Chinese hamster cell line, Don (2). In 1967 zur Hausen (3) described an appearance more often occurring in chromosome No. 1 and referred to as "incomplete condensation." The incompletely condensed segments were shown to synthesize DNA after the normal segments had ceased replication. Subsequently, both Nichols et al. (4) and Kato and Sandberg (5) have reported that pulverized chromosomes exhibit a similar asynchrony. The present report will provide evidence that pulverization, incomplete condensation, as well as some varieties of enhanced secondary constrictions form a spectrum of changes characterized by their spontaneous occurrence in permanent cell lines of several species and by DNA synthesis in G2 .