We have identified a gene involved in bacterial cell division, located immediately upstream of the ftsI gene in the min 2 region of the Escherichia coli chromosome. This gene, which we named ftsL , was detected through characterization of Tn phoA insertions in a plasmid containing this chromosomal region. Tn phoA topological analysis and fractionation of alkaline phosphatase fusion proteins indicated that the ftsL gene product is a 13.6-kDa cytoplasmic membrane protein with a cytoplasmic amino terminus, a single membrane-spanning segment, and a periplasmic carboxy terminus. The ftsL gene is essential for cell growth and division. A null mutation in ftsL resulted in inhibition of cell division, formation of long, nonseptate filaments, ultimate cessation of growth, and lysis. Under certain growth conditions, depletion of FtsL or expression of the largest ftsL-phoA fusion produced a variety of cell morphologies, including Y-shaped bacteria, indicating a possible general weakening of the cell wall. The FtsL protein is estimated to be present at about 20 to 40 copies per cell. The periplasmic domain of the protein displays a sequence with features characteristic of leucine zippers, which are involved in protein dimerization.

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The ftsQ gene is one of several genes thought to be specifically required for septum formation in Escherichia coli. Published work on the cell division behavior of ftsQ temperature-sensitive mutants suggested that the FtsQ product is required throughout the whole process of septum formation. Here we provide additional support for this hypothesis based on microscopic observations of the cell division defects resulting from insertional and temperature-sensitive mutations in the ftsQ gene, and constitutive overexpression of its gene product. On the basis of the published, predicted amino acid sequence of the FtsQ protein and our analysis of fusion proteins of the FtsQ protein to bacterial alkaline phosphatase, we conclude that FtsQ is a simple cytoplasmic membrane protein with a approximately 25-amino-acid cytoplasmic domain and a approximately 225-amino-acid periplasmic domain. We estimate that the FtsQ protein is present at about 22 copies per cell.

bor is one of two recently identified genes of phage which are expressed during lysogeny and whose products display homology to bacterial virulence proteins. bor is closely related to the iss locus of plasmid ColV,I-K94, which promotes bacterial resistance to serum complement killing in vitro and virulence in animals. bor has a similar in vitro effect. We show here that the bor gene product is a lipoprotein located in the Escherichia coli outer membrane. We also find that antigenically related proteins are expressed by lysogens of a number of other lambdoid coliphage, in cells carrying the cloned iss gene, and in several clinical isolates of E. coli. These results demonstrate that bor sequences are widespread and present a starting point for mechanistic analysis of bor-mediated serum resistance.Bacteriophage has long served as a model system for the study of fundamental biological processes, yet even now significant parts of biology remain poorly understood. One area of notable obscurity is the function of the so-called accessory sequences (16) which comprise roughly a third of the genome and are dispensable for growth and viability under laboratory conditions. These sequences contain numerous open reading frames of unknown function, and their retention in the face of presumably long-standing selective pressures suggests that they have functions which may provide consequential selective benefits.We have previously characterized two genes, lom and bor, whose distinctive features offer a novel perspective on the function of these accessory sequences and on the evolutionary significance of lysogeny by temperate phage generally (2). Both lom and bor are dispensable for phage vegetative growth, are expressed in Escherichia coli lysogens, and are related to bacterial virulence proteins. Lom is homologous to three such proteins, Ail, PagC, and Rck, which are involved in invasiveness of Yersinia enterocolitica, survival in macrophage phagosomes, and serum resistance of Salmonella typhimurium, respectively (23,35,46). A fifth member of the family, the Enterobacter cloacae protein OmpX, has not been associated with virulence properties (53, 54). None of these proteins is phage encoded.The phage bor gene is closely related to the iss locus of the conjugative plasmid ColV,I-K94. Sequencing (13) has shown that iss displays a discrete block of 796 bp of DNA homology to covering the region from bp 46186 to 46982 in the sequence (50), which is at the 3Ј end of R Z , at the extreme right end of the genome. On either side of this region, homology to is not detectable. The overall DNA identity between and iss is 81%, excluding gaps. The homologous region includes bor, 230 bp of 5Ј flanking DNA, and 274 bp of 3Ј flanking material which includes the coding region for the last 79 residues of R Z . Thus, iss appears to be a fragment of (or, less likely, vice versa), and it seems probable that the locus originated in a fairly recent recombination event between ColV,I-K94 and or a related phage. The iss open reading frame homologous to ...

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