A common step for changing cell shape in fruiting body and starvation-independent sporulation of Myxococcus xanthus.

Myxococcus xanthus can sporulate in either of two ways: at the end of the program of fruiting body development or after exposure of growing cells to certain reagents such as concentrated glycerol. Fruiting body sporulation requires starvation, while glycerol sporulation requires rapid growth, and since the two types of spores are structurally somewhat different, it has generally been assumed that the two processes are different. However, a Tn5 Lac insertion mutation, Omega7536, has been isolated which simultaneously blocks the development of fruiting body spores as well as glycerol-induced spores. Both sporulation pathways are blocked in the mutant within the process that converts a rod-shaped cell into a spherical spore. The Omega7536 locus is expressed at the time of cell shape change appropriate to each process, early after glycerol induction and late after starvation induction. On the C-signal response pathway, it is possible to identify positions for the normal function of the Omega7536 locus and for the inducing stimulus from glycerol that are unique and consistent with the observations. Although the two sporulation pathways differ in certain respects, it is shown that they share at least one step for changing a rod-shaped cell into a spherical spore.

SdeK is required for early fruiting body development in Myxococcus xanthus.

Myxococcus xanthus cells carrying the Omega4408 Tn5lac insertion at the sde locus show defects in fruiting body development and sporulation. Our analysis of sde expression patterns showed that this locus is induced early in the developmental program (0 to 2 h) and that expression increases approximately fivefold after 12 h of development. Further studies showed that expression of sde is induced as growing cells enter stationary phase, suggesting that activation of the sde locus is not limited to the developmental process. Because the peak levels of sde expression in both an sde+ and an sde mutant background were similar, we conclude that the sde locus is not autoregulated. Characterization of the sde locus by DNA sequence analysis indicated that the Omega4408 insertion occurred within the sdeK gene. Primer extension analyses localized the 5' end of sde transcript to a guanine nucleotide 307 bp upstream of the proposed start for the SdeK coding sequence. The DNA sequence in the -12 and -24 regions upstream of the sde transcriptional start site shows similarity to the sigma54 family of promoters. The results of complementation studies suggest that the defects in development and sporulation caused by the Omega4408 insertion are due to an inactivation of sdeK. The predicted amino acid sequence of SdeK was found to have similarity to the sequences of the histidine protein kinases of two-component regulatory systems. Based on our results, we propose that SdeK may be part of a signal transduction pathway required for the activation and propagation of the early developmental program.

The tyrosine kinase inhibitors, genistein and methyl 2,5-dihydroxycinnamate, inhibit the release of (3H)arachidonate from human platelets stimulated by thrombin or collagen.

We have investigated the effects of the tyrosine kinase inhibitors, genistein and methyl 2,5-dihydroxycinnamate, on [3H]arachidonic acid release from human platelets. Both tyrosine kinase inhibitors blocked, in a dose-dependent manner, the release of arachidonic acid stimulated by thrombin or suspensions of collagen fibres. Blockade by the tyrosine kinase inhibitors occurred early in the arachidonate release time course. Both genistein and methyl 2,5-dihydroxycinnamate also inhibited tyrosine phosphorylation in platelets. The inhibitors were specific in that they did not affect protein kinase C activity, ATP levels or mobilization of Ca2+ from internal stores. These findings suggest a role for tyrosine kinase activity in the regulation of phospholipase A2 in platelets stimulated by the physiological ligands, thrombin and collagen.