clpX encoding an alternative ATP-binding subunit of protease Ti (Clp) can be expressed independently from clpP in Escherichia coli.

ClpX, an alternative ATP-binding subunit for protease Ti (also called Clp), has been shown to support the ATP-dependent hydrolysis of lambda O-protein by ClpP. clpX has also been reported to be in an operon with clpP, and therefore both are co-transcribed in a single mRNA using the promoter proximal to clpP. Here, we show that clpX can be expressed independently from clpP using its own promoter. The cells carrying clpX alone on a multicopy plasmid successively produced the 46-kDa ClpX protein. Moreover, in vitro translation analysis revealed that the recombinant plasmid containing clpX generates the 46-kDa protein that can be immunoprecipitated with anti-ClpX antibody. In addition, it has recently been reported that CipX, but not ClpP, is required for normal replication of bacteriophage Mu. Thus, it appears that clpX can be expressed alone and/or co-expressed with clpP in cells depending on physiological conditions.