Cloning and characterization of ftsN, an essential cell division gene in Escherichia coli isolated as a multicopy suppressor of ftsA12(Ts)

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Abstract
A new cell division gene, ftsN, was identified in Escherichia coli as a multicopy suppressor of the ftsA12(Ts) mutation. Remarkably, multicopy ftsN suppressed ftsI23(Ts) and to a lesser extent ftsQ1(Ts); however, no suppression of the ftsZ84(Ts) mutation was observed. The suppression of ftsA12(Ts), ftsI23(Ts), and ftsQ1(Ts) suggests that FtsN may interact with these gene products during cell division. The ftsN gene was located at 88.5 min on the E. coli genetic map just downstream of the cytR gene. ftsN was essential for cell division, since expression of a conditional null allele led to filamentation and cell death. DNA sequence analysis of the ftsN gene revealed an open reading frame of 319 codons which would encode a protein of 35,725 Da. The predicted gene product had a hydrophobic sequence near its amino terminus similar to the noncleavable signal sequences found in several other Fts proteins. The presumed extracellular domain was unusual in that it was rich in glutamine residues. A 36-kDa protein that was localized to the membrane fraction was detected in minicells containing plasmids with the ftsN gene, confirming that FtsN was a membrane protein.