LATE DNA REPLICATION PATTERN IN HUMAN HAEMOPOIETIC CELLS - A COMPARATIVE INVESTIGATION USING A HIGH RESOLUTION QUANTITATIVE AUTORADIOGRAPHY

A quantitative autoradiographic technique was used to compare DNA duplication during the final phase of the synthesis period (about 30 min) in chromosomes of lymphocytes, erythroblasts and human bone marow cells. The duration of the G2 period in the three tissues was determined and a calculation was made in order to establish at which point before the beginning of this period each pair of chromosomes had completed synthesis. It was observed that the length of the single G2 period is very much the same in all three tissues. It was therefore possible to conclude that, in 19 chromosome pairs, synthesis will terminate in the last 10 min of the S period and in the other 5 pairs in the last 5 min. The synthetic activity rate of each pair of chromosomes, in the three types of haemopoietic cells, did not present significant differences either in the overall period or in the time intervals into which this period was subdivided (using time analysis based on a cumulative distribution method). Detection of late-labelling zones at the subchromosomic level, using a new technique, made it possible to obtain characteristic patterns for many chromosomes; but we were unable to detect qualitative or quantitative differences between the cells of different tissues. © 1968.