The size and number of replicon families of chromosomal DNA of Arabidopsis thaliana

Analysis of the replicon properties and the cell cycle ofArabidopsis thaliana (col.) at 22° C were performed via autoradiography of isolated chromosomal DNA fibers and single cells of seedlings. The cell cycle was 8.5 h and G1, S, and G2+1/2 M were 1.7, 2.8, and 4 h respectively. The average single fork rate was 5.8 m/h and the average replicon size was 24 m. The data best support the hypothesis that A. thaliana has two replicon families, one with approximately 687 and another with 1888 members per genome and that the families initiate replication in sequence separated by a 36 min interval. Replication of an average single replicon required a little more than 2 h or 74% of S and the 36 min interval between the initiation of replication by the two families constituted 21% of S.