Induction of a growth-phase-dependent promoter triggers transcription of bolA, an Escherichia coli morphogene.

The bolA gene, which is involved in the morphogenetic pathways of Escherichia coli, was sequenced and two potential promoters were identified. Expression from promoter P1, proximal to the bolA structural gene is specifically induced during the transition to the stationary phase of growth. This promoter contains an unusual--10 region (CGGCTAGTA), which defines a new class of E. coli promoters necessary for the dramatic increase in the rate of synthesis of a large set of proteins during the cessation of logarithmic growth. This conclusion was confirmed by identifying two additional E. coli promoters and one plasmid promoter, which also were induced during the transition to the stationary phase of growth. Analysis of proteins produced during the exponential and stationary phases of growth in a bolA null mutant suggest a possible role for the BolA protein in the induction of the expression of penicillin-binding protein 6 (PBP6) in the transition to the stationary phase. Supporting this hypothesis is the presence of a putative DNA-binding domain within the bolA coding sequence.     

Identification of new genes in a cell envelope-cell division gene cluster of Escherichia coli: cell division gene ftsQ.

We report the identification, cloning, and mapping of a new cell division gene, ftsQ. This gene formed part of a cluster of three division genes (in the order ftsQ ftsA ftsZ) which itself formed part of a larger cluster of at least 10 genes, all of which were involved in some step in cell division, cell envelope synthesis, or both. The ftsQAZ group was transcribed from at least two independent promoters.     

Evidence for functional overlap among multiple bacterial cell division proteins: compensating for the loss of FtsK

In Escherichia coli, at least 12 proteins colocalize to the cell midpoint, assembling into a membrane-associated protein machine that forms the division septum. Many of these proteins, including FtsK, are essential for viability but their functions in cell division are unknown. Here we show that the essential function of FtsK in cell division can be partially bypassed. Cells containing either the ftsA R286W mutation or a plasmid carrying the ftsQAZ genes suppressed a ftsK44(ts) allele efficiently. Moreover, ftsA R286W or multicopy ftsQAZ, which can largely bypass the requirement for the essential cell division gene zipA, allowed cells with a complete deletion of ftsK to survive and divide, although many of these ftsK null cells formed multiseptate chains. Green fluorescent protein (GFP) fusions to FtsI and FtsN, which normally depend on FtsK to localize to division sites, localized to division sites in the absence of FtsK, indicating that FtsK is not directly involved in their recruitment. Cells expressing additional ftsQ, and to a lesser extent ftsB and ftsN, were able to survive and divide in the absence of ftsK, although cell chains were often formed. Surprisingly, the cytoplasmic and transmembrane domains of FtsQ, while not sufficient to complement an ftsQ null mutant, conferred viability and septum formation in the absence of ftsK. These findings suggest that the N-terminal domain of FtsK is normally involved in stability of the division protein machine and shares functional overlap with FtsQ, FtsB, FtsA, ZipA and FtsN.     

Regulation of the expression of the cell-cycle gene ftsZ by DicF antisense RNA. Division does not require a fixed number of FtsZ molecules

We show that the 53-nucleotide RNA molecule encoded by gene dicF blocks cell division in Escherichia coli by inhibiting the translation of ftsZ mRNA. Such a role for dicF had been predicted on the basis of the complementarity of DicF RNA with the ribosome-binding region of the ftsZ mRNA. An analysis of ftsZ expression at its chromosomal locus, and of an ftsZ-lacZ translational fusion controlled by promoters ftsZ1p and ftsZ2p only, indicates that ftsZ is not autoregulated. Partial inhibition of FtsZ synthesis leads to increased cell size. However, the number of FtsZ molecules per cell can be reduced threefold without affecting the division rate significantly. Our results suggest that septation is not triggered by a fixed number of newly synthesized FtsZ molecules per cell.     

Regulation of septation and cytokinesis during resumption of cell division requires uvi31+, a UV-inducible gene of fission yeast

uvi31+ is a sequence homolog of Escherichia coli bolA gene in Schizosaccharomyces pombe, identified as a UV-inducible gene. Here, the cellular function of uvi31+ was investigated by null mutant analysis. Deletion of uvi31+ led to a delayed germination of spore and defects in subsequent cell division. However, the uvi31 mutant cell proliferated faster with smaller cell size than the wild-type cell during vegetative growth. In addition, the uvi31 mutant was sensitive to UV-light. It showed a normal cell cycle delay after UV-irradiation but displayed aberrant septum formation and defective cytokinesis when released from the UV damage checkpoint. These results suggest that uvi31+ may be involved in control of cell division, especially during the resumption from cell cycle arrest.     

Growth phase-regulated expression of bolA and morphology of stationary-phase Escherichia coli cells are controlled by the novel sigma factor sigma S.

The novel sigma factor (sigma S) encoded by rpoS (katF) is required for induction of many growth phase-regulated genes and expression of a variety of stationary-phase phenotypes in Escherichia coli. Here we demonstrate that wild-type cells exhibit spherical morphology in stationary phase, whereas rpoS mutant cells remain rod shaped and are generally larger. Size reduction of E. coli cells along the growth curve is a continuous and at least biphasic process, the second phase of which is absent in rpoS-deficient cells and correlates with induction of the morphogene bolA in wild-type cells. Stationary-phase induction of bolA is dependent on sigma S. The "gearbox" a characteristic sequence motif present in the sigma S-dependent growth phase- and growth rate-regulated bolAp1 promoter, is not recognized by sigma S, since stationary-phase induction of the mcbA promoter, which also contains a gearbox, does not require sigma S, and other sigma S-controlled promoters do not contain gearboxes. However, good homology to the potential -35 and -10 consensus sequences for sigma S regulation is found in the bolAp1 promoter.     

Insights into the CtrA regulon in development of stress resistance in obligatory intracellular pathogen Ehrlichia chaffeensis

Ehrlichia chaffeensis is an obligate intracellular bacterium that causes human monocytic ehrlichiosis. Ehrlichiae have a biphasic developmental cycle consisting of dense-cored cells (DCs) and reticulate cells (RCs). Isolated DCs are more stress resistant and infectious than RCs. Here, we report that a response regulator, CtrA was upregulated in human monocytes at the late growth stage when DCs develop. E. chaffeensis CtrA bound to the promoters of late-stage transcribed genes: ctrA, ompA (peptidoglycan-associated lipoprotein), bolA (stress-induced morphogen) and surE (stationary-phase survival protein), which contain CtrA-binding motifs, and transactivated ompA, surE and bolA promoter-lacZ fusions in Escherichia coli. OmpA was predominantly expressed in DCs. E. chaffeensis binding to and subsequent infection of monocytes were inhibited by anti-OmpA IgG. E. chaffeensis BolA bound to the promoters of genes encoding outer surface proteins TRP120 and ECH_1038, which were expressed in DCs, and transactivated trp120 and ECH_1038 promoter-lacZ fusions. E. chaffeensis bolA complemented a stress-sensitive E. coli bolA mutant. E. coli expressing E. chaffeensis SurE exhibited increased resistance to osmotic stress. Our results suggest that E. chaffeensis CtrA plays a role in co-ordinating development of the stress resistance for passage from the present to the next host cells through its regulon.     

Effect of Escherichia coli morphogene bolA on biofilms

Biofilm physiology is established under a low growth rate. The morphogene bolA is mostly expressed under stress conditions or in stationary phase, suggesting that bolA could be implicated in biofilm development. In order to verify this hypothesis, we tested the effect of bolA on biofilm formation. Overexpression of bolA induces biofilm development, while bolA deletion decreases biofilms.     

Mutation in the structural gene for release factor 1 (RF-1) of Salmonella typhimurium inhibits cell division.

A temperature-sensitive mutant of Salmonella typhimurium LT2 was isolated. At the nonpermissive temperature cell division stopped and multinucleated filaments were formed. DNA, RNA, or protein synthesis was not affected until after about two generations. Different physiological conditions, such as anaerobiosis and different growth media, suppress the division deficiency at high temperatures. Certain mutations causing a reduced polypeptide chain elongation rate also suppress the division deficiency. The mutation is recessive and shown to be in the structural gene for release factor I (prfA). DNA sequencing of both the wild-type (prfA+) and mutant (prfA101) allele revealed a GC-to-AT transition in codon 168. Like other known prfA mutants, prfA101 can suppress amber mutations. The division defect in the prfA101 mutant strain could not be suppressed by overexpression of the ftsQAZ operon. Moreover, at the nonpermissive temperature the mutant shows a normal heat shock and SOS response and has a normal ppGpp level. We conclude that the prfA101-mediated defect in cell division is not directed through any of these metabolic pathways, which are all known to affect cell division. We speculate that the altered release factor I induces aberrant synthesis of an unidentified protein(s) involved in the elaborate process of septation.     

NONESSENTIALITY OF CONCURRENT CELL DIVISIONS FOR DEGREE OF POLARIZATION OF LEAF GROWTH. II. EVIDENCE FROM UNTREATED PLANTS AND FROM CHEMICALLY INDUCED CHANGES OF THE DEGREE OF POLARIZATION

Haber, Alan H., and D. E. Foard. (Oak Ridge Natl. Lab., Oak Ridge, Tenn.) Nonessentiality of concurrent cell divisions for degree of polarization of leaf growth. II. Evidence from untreated plants and from chemically induced changes of the degree of polarization. Amer. Jour. Bot. 50(9): 937–944. Illus. 1963.—Tobacco leaves grow with a constant degree of polarization (i.e., ratio of rate of increase in length per mm length to rate of increase in width per mm width). During this growth there is decreasing mitotic activity. Data from the literature, including Sinnott's classic studies with cucurbit fruits, provide additional specific examples of growth of (1) constant degree of polarization during which (2) mitotic activity falls. The generalization that cell division plays no role in maintaining a constant degree of polarization is suggested by the widespread occurrence of these 2 features of growth in determinate organs. These considerations are consistent with our earlier finding that the degree of polarization of growth of the first foliage leaf of wheat is the same in seedlings normally growing with oriented cell divisions and in gamma-plantlets, which are seedlings growing without cell division owing to gamma-irradiation of the grain before sowing. The present work shows that the degree of polarization can be significantly increased by treatment with gibberellic acid and decreased by colchicine, even though it is unaffected by radiation-induced mitotic inhibition. These chemically induced changes in the degree of polarization are, moreover, the same in unirradiated and in gamma-plantlet leaves. We conclude that cell division is essential neither for maintaining the degree of polarization nor for changing the degree of polarization. These considerations lead to 3 biological conclusions, each of which is in harmony with simple geometric considerations: (1) cell divisions do not directly contribute to or cause growth; (2) cell division plays an essential and immediate role in influencing cell forms, but plays a secondary and much less important role in influencing organ form; and (3) there is a fallacy in the usual and accepted manner of interpreting changes in organ size as being due to changes in cell size and changes in cell number.