The sdeK gene is essential to the Myxococcus xanthus developmental process,
We reported previously, based on sequence analysis (A. G, Garza, J, S, Pol
lack, B, Z, Harris, A. Lee, I, M, Keseler, E, F, Licking, and M, Singer, J,
Bacteriol. 180:4628-4637, 1998), that SdeK appears to be a histidine kinas
e, In the present study, we have conducted both biochemical and genetic ana
lyses to test the hypothesis that SdeK is a histidine kinase, An SdeK fusio
n protein containing an N-terminal polyhistidine tag (His-SdeK) displays th
e biochemical characteristics of a histidine kinase, Furthermore, histidine
286 of SdeK, the putative site of phosphorylation, is required for both in
vitro and in vivo protein activity, The results of these assays have led u
s to conclude that SdeK is indeed a histidine kinase, The developmental phe
notype of a Delta sdeK1 strain could not be rescued by codevelopment with w
ild-type cells, indicating that the defect is not due to the mutant's inabi
lity to produce an extracellular signal. Furthermore, the Delta sdeK1 mutan
t was found to produce both A- and C-signal, based on A-factor and codevelo
pment assays with a csgA mutant, respectively. The expression patterns of s
everal Tn5lacZ transcriptional fusions were examined in the Delta sdeK1-nul
l background, and we found that all C-signal-dependent fusions assayed also
required SdeK for full expression. Our results indicate that SdeK is a his
tidine kinase that is part of a signal transduction pathway which, in conce
rt with the C-signal transduction pathway, controls the activation of devel
opmental-gene expression required to progress past the aggregation stage.