Purification and characterization of the CheZ protein of bacterial chemotaxis

The cheZ gene is the most distal of five genes that comprise the Meche operon of the Salmonella typhimurium chemotaxis system. We have determined the sequence of the cheZ gene along with an 800-nucleotide flanking region at its 3' end. The flanking sequence contains an open reading frame that probably corresponds to the 5' end of flaM. The cheZ coding sequence predicts an extremely acidic, hydrophilic protein with a molecular weight of 23,900. We have purified and characterized this protein. N-terminal analysis of pure CheZ yields an amino acid sequence identical to that predicted by the nucleotide sequence except that the amino-terminal methionine residue is modified by N methylation. The purified CheZ protein exhibits a native molecular weight of 115,000, but in cell extracts the majority of CheZ exists as a much larger aggregate (Mr greater than 500,000). Under these conditions, CheZ appears to be a homopolymer composed of at least 20 monomeric subunits.