IDENTIFICATION AND CHARACTERIZATION OF FRZZ, A NOVEL RESPONSE REGULATOR NECESSARY FOR SWARMING AND FRUITING-BODY FORMATION IN MYXOCOCCUS-XANTHUS

The frz genes of Myxococcus xanthus constitute a signal-transduction p athway that processes chemotactic information in a manner analogous to that found in enteric bacteria. Ultimately, these genes regulate the frequency of individual cell reversal. We report here the identificati on of a novel component of this signal-transduction pathway, designate d frzZ,which was discovered as an open reading frame located 5' to the frz operon but transcribed in the opposite orientation. The translati onal start site of frzZ is 170 base pairs from that of frzA. frzZ util izes a promoter similar to the sigma(70) promoters of Escherichia coli , and encodes a 290-amino-acid soluble protein, FrzZ (M(r) 30 500). Fr zZ contains two domains, both of which show strong homology to CheY an d other members of the response-regulator family. Linking these domain s is a 39-amino-acid region that is very rich in alanine and proline ( 38% Ala and 33% Pro). A frzZ null mutant showed abnormally low reversa l rates when compared to the wildtype control and was unable to form f ruiting bodies on starvation medium, but it did form 'frizzy' aggregat es. In addition, the frzZ mutant was defective in swarming, particular ly on soft agar (0.3% w/v). However, unlike most frz mutants, the frzZ mutant was able to respond to attractants and repellents in the spati al chemotaxis assay. The discovery of FrzZ demonstrates that the M. xa nthus frz signal-transduction pathway utilizes multiple response-regul ator (CheY-like) proteins.