THE DIFFERENTIAL CAPACITY FOR RNA SYNTHESIS AMONG CHROMOSOMES: A CYTOLOGICAL APPROACH

Abstract

Chromosome breakages were induced in Chinese hamster cells in vitro by X rays, tritiated thymidine, and tritiated uridine. X irradiation induced a random distribution of breaks, both along individual chromosomes and between different chromosomes. The distribution of breaks induced by tritiated thymidine was correlated closely with the DNA replication activity of the chromosome. Breakages induced by tritiated uridine were not distributed at random, with the Y chromosome being most resistant, and the early DNA replicating sites most susceptible. Although the possibility of retention of RNA at the site of the transcription cannot be ignored, the phenomenon is more likely the result of differential capacity for RNA synthesis among the chromosomes.