Characteristics of Infection by RSV. I. Non-Requirement for the S Phase of Cellular DNA Synthesis

Abstract

The relationship between the position of chick embryo fibroblasts in the mitotic cycle and their susceptibility to infection by B-RSV (RAVI) was studied in synchronized cultures. The pattern of virus growth was similar in cultures infected at various times during the mitotic cycle. Notably, first virions were released after comparable delays in cultures infected before, during or after the S phase, and the virus production was identical when measured up to 48 h after infection. Latent periods extended from 8 to 15 h according to the experiment. Identical results were obtained with both calf sera used to induce mitoses. These results show that the S phase of cellular DNA synthesis is not required at some early stage of the viral cycle and suggest that there is no obligatory relationship between RSV production and the cell cycle.

Characteristics of Infection by RSV. II. Dependence on Cell Events which Can Occur in the G2 Phase and after Mitosis

“…[3] or by our method [I], and infected with different amounts of B-RSV (RAVI) at various times in the cell cycle. All experiments were performed in the presence of a particular batch of calf scrum (13) distinct from those previously used [1], The results were the same with both methods of synchronization, regard less of the MOI, and they support our previous conclusion that cell DNA replication is not required at some early stage of the infection. In addition, they show that successful infection depends on cell events which can occur in a synchronous manner in the G2 phase and/or after the cell division (phase M), on the condition that some factor(s) are present in the calf serum used.…”

“…This was measured after labelling of cultures with 20 p.Ci 3H-thymidine in 0.5 ml o f medium 2 [1] and incubating them for 15 min at 39°.…”

“…The synchronization of cells was accomplished using two distinct procedures: first, cells were synchronized according to our method described in the preceding paper [ 1 ]; in this case, the time of induction of the cell division corresponded to the time o f addition o f calf serum. Second, cells were synchronized according to the method described by Hobom-Schnegg et at.…”

“…Other materials and methods were the same as in the preceding paper [1]. In particular, synchronized cells were infected with the same partially purified B-RSV (RAVI).…”

“…In the preceding paper [1], we have shown that the S phase of cellular DNA replication is not required for successful infection by RSV. This finding appeared to be in conflict with results reported by other investigators [2,3] and the hypothesis was put forward that such a discrepancy could be related to differences between experimental conditions.…”