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

Abstract

Chick embryo fibroblasts synchronized in two different ways were infected at various times in the cell cycle with B-RSV (RAVI) in the presence of a particular calf serum. In all experiments, with both methods of synchronization, the length of the latent period depended on when cells were infected in the cell cycle. In cultures infected in the G1 and S phases, the production of the virus was delayed until the phase G2 or after the cell division, depending on what method was used to synchronize cells. In cultures infected after the G2 phase, the production of the virus was delayed until after cell division. It is concluded that cell event(s) are required at some stage of the infection for it to be successful; they can occur in a synchronous manner in the G2 phase, before replication of the mitochondrial DNA, and after the wave of mitoses when some component(s) are present in the calf serum used to induce the cell division.

Characteristics of Infection by RSV

“…Earlier times were not explored. These results agree with our previous findings on synchron ized cells [1]. In addition, they suggest that the presence o f RAVI does not significantly shorten some step o f the virus cycle.…”

“…The present experiments were carried out to check and eventually to con firm our previous observation that the duration of the latent period of RSV can be as short as 2 h [1], In the first series of experiments, the new virions of SR-RSV belonged to the A subgroup as result of the phenotypic mixing occurring between the input virus and RAVI. It was seen that these new virions were efficiently neutralized by anti-RAVl serum.…”

“…This condition was ful filled by infecting cells blocked in the early G1 phase of the cell division cycle as a result of both aging and confluence. Indeed, our previous results [1 ] showed that viral synthesis can start only in dividing cells from the G2 and M phases. Experimental procedure was exactly the same as used in experiments 2 and 3 except that infection was carried out on confluent secondary cultures (4-10® cells per dish) subcultured 3 days previously.…”

“…Later experiments were performed with a high titer clonal strain of SR-RSV (D) obtained from Dr. Boettiger (Imperial Cancer Research Fund Laboratories, London). Both viruses were used after concentration from culture media as already described [1], Their titers were 106 and 1.3 x 107 FFU/ml, respec tively. The MOI was 0.1-0.2 FFU/cell.…”

“…In the previous paper of this series [1] it was calculated that the duration of the latent period of the Bryan strain of Rous sarcoma virus (B-RSV; RAVI) in synchronized chicken cells could be as short as 2 h in cultures infected during the G2 phase o f the cell division cycle. The hypothesis was raised that cell events required at some early step of the virus cycle had occurred during this phase.…”