SYNCHRONOUS REPLICATION OF SV 40 DNA IN VIRUS-INFECTED TC 7 CELLS INDUCED BY TRANSIENT HYPOXIA

We transiently exposed SV 40 infected TC 7 cell cultures to a reduced O-2 tension (4-8 h, about 200 ppm relative to 10(5) Pa total pressure) . Under the hypoxic conditions, 'working' viral replication forks were greatly retarded or stopped, and initiation of daughter strand synthe sis in further SV 40 DNA molecules was suppressed. Reoxygenation relea sed an immediate burst of SV 40 replication which mainly consisted of a synchronous viral replication round. This synchronous in vivo replic ation began at the known origin of replication and proceeded at normal rates to the known termination region. Viral replicons seemed to accu mulate under hypoxia in a state fully prepared to begin replication im mediately after recovery of a normal pO(2). The shut-down and sudden r eactivation of DNA synthesis under hypoxia and reoxygenation, respecti vely, were not accompanied by changes of the phosphorylation state of large T antigen. The described synchronization procedure can be applie d to optionally large SV 40 infected cell cultures.