SDEK IS REQUIRED FOR EARLY FRUITING BODY DEVELOPMENT IN MYXOCOCCUS-XANTHUS

Myxococcus xanthus cells carrying the Omega 4408 Tn5lac insertion at t he sde locus show defects in fruiting body development and sporulation . Our analysis of sde expression patterns showed that this locus is in duced early in the developmental program (0 to 2 h) and that expressio n increases approximately fivefold after 12 h of development. Further studies showed that expression of sde is induced as growing cells ente r 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. Characterizatio n of the sde locus by DNA sequence analysis indicated that the Omega 4 408 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 transcriptiona l start site shows similarity to the sigma(54) family of promoters. Th e results of complementation studies suggest that the defects in devel opment and sporulation caused by the Omega 4408 insertion are due to a n inactivation of sdeK. The predicted amino acid sequence of SdeK was found to have similarity to the sequences of the histidine protein kin ases of tao-component regulatory systems. Based on oar results, we pro pose that SdeK may be part of a signal transduction pathway required f or the activation and propagation of the early developmental program.