Virus‐induced premature chromosome condensation (PCC) in single cells and G‐bands of PCC‐chromatin

Premature chromosome condensation, PCC (formerly called pulverization), is due to an asynchrony between two or more chromosome sets within a common cytoplasm of which one is at metaphase stage and apparently forces the lagging nuclear component to enter a precocious condensation for metaphase. Single metaphase cells in which some of the chromosomes show PCC were produced by treatment of human lymphocyte cultures with live Sendai virus a few hours prior to harvest. The morphology of PCC in these cells was predominantly of prophase‐like PCC type originating from G2 cells, whereas PCC type from G1 cells was not seen in partial PCC cells. G‐band procedure (ASG‐technique) produced clear, darkly stained chromatin segments (bands) in PCC from G1 as well as G2 types. PCC of the pulverization type, originating from S‐phase cells, showed no band‐like structures. G‐bands of the intact metaphase chromosomes in partial PCC cells were less clear than in normal cells, and therefore the missing chromosomes, i.e. the PCC chromosomes, could not be identified in a large proportion of PCC cells. The Y‐chromosome was, however, affected more often than expected on the basis of a random distribution of partial PCC, suggesting that late labeling chromosomes are more susceptile to the virus‐induced chromatin change.