Nucleic Acids Research, 1978, Vol. 5, No. 9 3303-3314
© 1978
Articles |
DNA replication in Physarum polycephalum: UV photolysis of maturing 5-bromo-deoxyuridine substituted DNA
Institute of Medical Biology, University of Tromsø 9000 Tromsø, Norway
Received July 10, 1978. Combinations of 5-bromodeoxyuridine (BrdUrd) and 3H-de-oxyadenosine (3H-dAdo) short pulses were given in the synchronous DNA-replication period of Physarum polycephalum. After a chase period, UV-photolysis products were analysed on alkaline sucrose gradients. This strategy has allowed the following conclusions:
a) at the time of master-initiation of DNA replication, points separated by 1.12.2x107 daltons of single strand DNA may initiate DNA synthesis.
b) among these, only selected groups of replicons actually proceed in DNA replication at this time, while others appear to hold (later temporal sets of replicons). The origins of the ones that proceed in replication are separated from each other by a distance corresponding to 1.12.2x107 daltons.
c) regions in actual replication are separated from each other by increasing distances (up to 1.5x108 daltons single strand DNA) at later times in S.