Analysis of a myosin-like protein and the role of calcium in the E. coli cell cycle.

For a number of years now, we have argued that current models for the control of initiation of DNA synthesis, chromosomal partitioning and septum formation in Escherichia coli are unsatisfactory. Indeed, we could argue that despite considerable efforts, with the possible exception of dnaA and ftsZ, no genes specifically implicated in these control processes have been identified. In the cases of DnaA and FtsZ, no evidence has appeared to indicate how such molecules might be regulated to act once per cycle. In 1988, we formulated a specific proposal that the timing of cell cycle events in E. coli might be determined by a Ca++ flux, mediated by calcium-binding proteins and protein kinases and culminating, in the case of chromosome segregation and division, in the action of force-generating proteins such as myosin (Norris et al., 1988). In formulating this proposal, we took the view that the fundamental elements of cell cycle regulation are likely to be highly conserved across all species including prokaryotes. In this presentation, we shall describe the approaches we have been taking in order to test this hypothesis and to summarize the data obtained, in particular in relation to new genes identified which may play a role in the E. coli cell cycle. We shall also briefly indicate recent data from other laboratories consistent with our general hypothesis.

Inhibition of thrombocytopenic petechiae by exogenous serotonin administration.

The effect of serotonin on vascular fragility, visible as petechiae, was examined in antiplatelet serum-induced thrombocytopenic hamsters. Serotonin was administered intravenously or intraperitoneally, and following a single injection of 0.5 mg/100 g body weight, a temporary inhibition of petechial formation for approximately 1 h was observed. Repeated serotonin injections maintained animals free of petechiae for the 4-hour period of administration. Plasma levels of serotonin and the effect of serotonin on cutaneous perfusion were not significant factors in the observed inhibition of petechiae. The data suggest that in normal animals platelet serotonin may contribute more to maintaining microvascular structural integrity than platelet adhesion.