REGULATION OF MOTILITY BEHAVIOR IN MYXOCOCCUS-XANTHUS MAY REQUIRE AN EXTRACYTOPLASMIC-FUNCTION SIGMA-FACTOR

Using interaction trap technology, we identified a putative extracytop lasmic-function (ECF) sigma factor (RpoE1) in Myxococcus xanthus, a ba cterium which has a complex life cycle that includes fruiting body for mation. The first domain of the response regulator protein FrzZ, a com ponent of the Frz signal transduction system, was used as bait. Althou gh the RpoE1 protein displayed no interactions with control proteins p resented as bait, a weak interaction with a second M. xanthus response regulator (AsgA) was observed. While the specificity of the FrzZ-RpoE 1 interaction therefore remains speculative, cloning and sequencing of the region surrounding rpoE1 localized it to a position downstream of the frzZ gene. A potential promoter site for binding of an ECF sigma factor was identified upstream of rpoE1, suggesting the gene may be au toregulated. However, primer extension studies suggested that transcri ption of rpoE1 occurs under both vegetative and developmental conditio ns from a sigma(70)-like promoter. not blot analysis of RNA preparatio ns confirmed the low-level, constitutive expression of rpoE1 during bo th stages of the life cycle. Analysis of an insertion mutant also indi cated a role for RpoE1 under both vegetative and developmental conditi ons, since swarming was reduced on nutrient-rich agar and developmenta l aggregation was effected under starvation conditions, especially at high cell densities. An insertion mutation introduced into the gene di rectly downstream of rpoE1 (orf5) did not result in either swarming or developmental aggregation defects, even though the gene is transcribe d as part of the same operon. Therefore, we propose that this new ECF sigma factor could play a role in the transcriptional regulation of ge nes involved in motility behavior during both stages of the complex M. xanthus life cycle.