Deletion of the yhhP gene results in filamentous cell morphology in Escherichia coli

The Escherichia coli yhhP gene was predicted to encode a small hypothetical protein of 81 amino acids, the cellular function of which is not known. To gain insight into the function of this uncharacterized YhhP protein, genet ic and biochemical studies were done. We first tried to express and purify the YhhP protein to prepare an anti-YhhP antiserum. Western blotting showed that the hypothetical yhhP gene is indeed transcribed and translated as a minor cytoplasmic protein. YhhP-deficient (Delta yhhP) cells formed colonie s poorly on a rich medium (e.g., Luria-Bertani medium) containing a relativ ely low concentration of NaCl, while they can grow normally either in LB co ntaining 3% NaCl or in a synthetic medium (e.g., M9-glucose). During expone ntial growth in rich medium, an early step of cell division was inhibited i n Delta yhhP cells, forming filaments. For the YhhP-deficient filamentous c ells, the FtsZ-ring formation was analyzed with immunofluorescence microsco py. The FtsZ-ring formation did not occur normally in the Delta yhhP filame nts, although the filamentous cells contained the FtsZ protein at a certain level comparable to that in the wild-type cells. The ftsZ gene was found t o function as a multicopy suppressor of the Delta yhhP mutant. Another mult icopy suppressor gene was identified as the dksA gene. Provided that either the ftsZ or dksA gene was introduced into the mutant cells with its multic opy state, the resulting transformants were capable of growing in rich medi um, formed wild-type short rods. These results are discussed with regard to the presumed function of this ubiquitous protein.