Cloning, sequencing, and characterization of multicopy suppressors of a mukB mutation in Escherichia coli

Abstract

The mukB gene codes for a 177kDa protein, which might be a candidate for a force‐generating enzyme in chromosome positioning in Escherichia coli. The mukB106 mutant produces normal‐sized, anucleate cells and shows a temperature‐sensitive colony formation. To Identify proteins interacting with the MukB protein, we isolated three multicopy suppressors (msmA, msmB, and msmC) to the temperature‐sensitive colony formation of the mukB106 mutation. The msmA gene, which could not suppress the production of anucleate cells, was found to be identical to the dksA gene. The msmB and msmC genes suppressed the production of anucleate cells as well as the temperature‐sensitive colony formation. However, none of them couid suppress both phenotypes in a mukB null mutation. DNA sequencing revealed that the msmB gene was identicai to the cspC gene and that the msmC gene had not been described before. A homology search revealed that the amino acid sequences of both MsmB and MsmC possessed high similarity to proteins containing the cold‐shock domain, such as CspA of E. coliand the Y‐box binding proteins of eukaryotes; this suggests that MsmB and MsmC might be DNA‐binding proteins that recognize the CCAAT sequence. Hence, the msmB and msmC genes were renamed cspC and cspE, respectively. Possible mechanisms for suppression of the mukB106 mutation are discussed.