Factors influencing replicon organization in tissues having different S-phase durations in the mole rat, Bandicota...

In order to identify factors affecting the length of S-phase in mammals, DNA fibre autoradiograms from different tissues [bone marrow, phytohaemagglutinin (PHA)-stimulated spleen lymphocytes and whole body cells of new-borns] of the mole rat, Bandicota bengalensis, were examined for various parameters of replicon organization. The duration of S-phase in bone marrow and spleen was 12-14 h while that in new-borns was 8-9 h. Fork migration rate was significantly greater in new-borns than in bone marrow, and replicon size was significantly smaller in new-borns than in spleen. Thus it appears that several factors contribute, to varying degrees, in establishing the duration of S-phase in any cell type. In about 20% of the replicon clusters, constituent replicons were found to initiate replication asynchronously. This asynchronous initiation could possibly be due to an effect of transcription on time of initiation since it is likely that neighbouring replicons would be transcribed to different extents.