The Frz pathway of Myxococcus xanthus controls cell reversal frequency to support directional motility during swarming (right images) and fruiting body formation (lower left). The frequency of cell reversals is correlated with phosphorylation of the response regulator FrzZ. The cognate histidine kinase FrzE also contains a response regulator domain that functions as a negative regulator of kinase activity, an effect modulated by FrzZ. For details, see the article by Kaimer et al. on pp. 379–395 of this issue. Issue 2 (April 2016) - Unknown