Biomedical subjects

A Driks

Publications and source records attributed to A Driks.

29 records · Page 2Linked to original sources

PubMed1993

Sporulation gene spoIIB from Bacillus subtilis.

We have cloned and characterized the sporulation gene spoIIB from Bacillus subtilis. In extension of previous nucleotide sequence analysis, our results show that the order of genes in the vicinity of spoIIB is valS folC comC spoIIB orfA orfB mreB mreC mreD minC minD spoIVFA spoIVFB L20 orfX L24 spoOB obg pheB pheA. All 20 genes have the same orientation; the direction of transcription is from valS to pheA. We show that spoIIB is a 332-codon-long open reading frame whose transcription is under sporulation control. The deduced amino acid sequence of the spoIIB gene product, a 36-kDa polypeptide, is highly charged and contains a stretch of uncharged amino acids that could correspond to a transmembrane segment. Surprisingly, mutations in spoIIB, including an in vitro-constructed null mutation, cause only a mild impairment of spore formation in certain otherwise wild-type bacteria. However, when combined with mutations in another sporulation gene, spoVG, mutations in spoIIB cause a severe block in spore formation at the stage (stage II) of septum formation. (As with spoIIB mutations, mutations in spoVG cause little impairment in sporulation on their own.) The nature of the spoIIB spoVG mutant phenotype is discussed in terms of the events involved in the maturation of the sporulation septum and in the activation of sporulation transcription factors sigma F and sigma E.

Amino Acid Sequence↗

PubMed1993

Cloning and characterization of a gene required for assembly of the Bacillus subtilis spore coat.

During endospore formation in Bacillus subtilis, approximately a dozen proteins are synthesized and assembled around the prespore to form a protective coat. Little is known about the assembly process, but several of the genes encoding these coat proteins are expressed in the mother cell compartment, where the proteins accumulate on the outer side of the developing endospore. Transcription of these genes is directed by the mother cell-specific sigma factor, sigma K, during the later stages of endospore development. sigma E may direct expression of the genes that encode proteins that function in the earliest stages of coat assembly. By screening for sigma E-dependent promoters, we cloned a gene, designated spoVID, required for assembly of a normal spore coat. Expression of spoVID was initiated at about the second hour of sporulation and continued throughout development from a sigma E-dependent promoter. The spoVID gene was located on the B. subtilis chromosome just downstream of the previously characterized hemAXCDBL operon and is predicted to encode an extremely acidic protein with 575 residues. Insertion mutants of spoVID produced refractile spores that were resistant to heat and to chloroform but were sensitive to lysozyme. Electron microscopic examination of sporulating spoVID mutant cells revealed normal morphological development up to about the third hour of sporulation. However, during the later stages of development the coat proteins assembled into aberrant structures that occurred freely in the mother cell cytoplasm and that consisted of reiterations of the single inner and outer layers that normally make up the spore coat.

Amino Acid Sequence↗

PubMed1992

Characterization of spoIVA, a sporulation gene involved in coat morphogenesis in Bacillus subtilis.

We report the cloning and characterization of the Bacillus subtilis sporulation locus spoIVA, mutations at which cause an unusual defect in spore formation in which the coat misassembles as swirls within the mother cell. We show that spoIVA is a single gene of 492 codons that is capable of encoding a polypeptide of 55 kDa. Transcription of spoIVA is induced at about the second hour of sporulation by the regulatory protein sigma E from two closely spaced promoters designated P1 and P2. Experiments in which the upstream promoter P1 was removed show that transcription of spoIVA from P2 is sufficient for efficient spore formation. Based on these and other findings, we infer that the spoIVA gene product is a morphogenetic protein; we discuss its role in the deposition of coat polypeptides around the developing forespore.

Amino Acid Sequence↗

PubMed1991

Compartmentalized expression of a gene under the control of sporulation transcription factor sigma E in Bacillus subtilis.

Immunoelectron microscopy was used to visualize the expression of a gene under the control of developmental transcription factor sigma E during spore formation in Bacillus subtilis. sigma E is generated by cleavage of an inactive proprotein (pro-sigma E) shortly after the formation of the sporulation septum, which partitions the sporangium into mother-cell and forespore compartments. Specific antibodies and gold-conjugated secondary antibodies were used to localize beta-galactosidase in thin sections of sporangia from cells bearing a lacZ transcriptional fusion to a gene (spoIID) under the direct control of sigma E. Transcription of spoIID was found to be induced shortly after the formation of the sporulation septum and was largely confined to the mother cell. Cell-type-specific transcription of genes under the control of sigma E could be responsible for establishing the mother-cell line of gene expression.

Bacillus subtilis↗

PubMed1991

Establishment of cell type by compartmentalized activation of a transcription factor.

Early in the process of spore formation in Bacillus subtilis a septum is formed that partitions the sporangium into daughter cells called the forespore and the mother cell. The daughter cells each have their own chromosome but follow dissimilar programs of gene expression. Differential gene expression in the forespore is now shown to be established by the compartmentalized activity of the transcription factor sigma F. The sigma F factor is produced prior to septation, but is active only in the forespore compartment of the post-septation sporangium. The sigma F factor is controlled by the products of sporulation operons spoIIA and spoIIE, which may be responsible for confining its activity to one of the daughter cells.

Bacillus subtilis↗

PubMed1991

Differentiation and the establishment of cell type during sporulation in Bacillus subtilis.

Differentiation in Bacillus subtilis involves the formation of specialized cell types called the mother cell and the forespore. These differ from each other and from their parent in developmental fate. Establishment of the two cell types and their subsequent differentiation is governed by the compartmentalized action of six developmental transcription factors.

Bacillus subtilis↗

PubMed1991

Forespore-specific transcription of a gene in the signal transduction pathway that governs Pro-sigma K processing in Bacillus subtilis.

We present studies on the regulation of a developmental gene (spoIVB) whose product is required at a late stage of morphogenesis during the process of sporulation in Bacillus subtilis. Earlier work implicated the spoIVB gene product in a signal-transduction pathway that governs the conversion of pro-sigma K to the mature and active form of the mother cell sigma factor, sigma K, in response to a signal generated within the forespore chamber of the sporangium. We now show that (1) spoIVB is induced at the engulfment stage of sporulation, (2) this transcription is restricted to the forespore, and (3) spoIVB is under the direct control of the forespore sigma factor sigma G. The discovery that spoIVB is a forespore-expressed gene suggests that the spoIVB gene product, or a developmental event under its control, triggers the processing of pro-sigma K and thereby mediates the coupling of sigma K-directed gene expression in the mother cell to sigma G-directed gene expression in the forespore. We also show that spoIVB transcription is partially dependent on the action of the mother cell regulatory gene spoIIID, a finding that suggests that the transcription of certain forespore-expressed genes is influenced by events in the mother cell.

Bacillus subtilis↗

PubMed1990

A forespore checkpoint for mother cell gene expression during development in B. subtilis.

Gene expression in the mother cell compartment of sporulating cells of B. subtilis is partly governed by the mother cell RNA polymerase sigma factor sigma K. Paradoxically, sigma K-directed gene expression also depends on sigma G, the product of the forespore compartment regulatory gene spoIIIG, and on other forespore regulatory proteins. We now identify mutations in the genes bofA and bofB that relieve the dependence of mother cell gene expression on forespore regulatory proteins but not on sigma K. We establish that the dependence of mother cell gene expression on the forespore regulatory proteins is mediated at the level of the conversion of pro-sigma K to its mature, active form. We propose that the bofA and/or bofB proteins govern this conversion in response to a signal generated by the forespore. Activation of pro-sigma K could be a checkpoint for coordinating gene expression between the mother cell and forespore compartments of the developing sporangium.

Bacillus subtilis↗

PubMed1990

Additional structures associated with bacterial flagellar basal body.

By fixation of preparations prior to negative staining, we have been able to visualize additional features attached to the basal body of Salmonella typhimurium. These new features consist of arms attached to the M ring, a cap resting atop the arms, and a dome attached to the rod. These structures may be parts of the motor and/or of the putative, flagellar export apparatus. Preparations from mutant strains show that the presence of these features does not depend on the presence of the motA, motB or cheA genes.

Flagella↗

PubMed1990

A Caulobacter gene involved in polar morphogenesis.

At specific times in the cell cycle, the bacterium Caulobacter crescentus assembles two major polar organelles, the flagellum and the stalk. Previous studies have shown that flbT mutants overproduce flagellins and are unable to form chemotaxis swarm rings. In this paper, we report alterations in both the stalk and the flagellar structure that result from a mutation in the flagellar gene flbT. Mutant strains produce some stalks that have a flagellum, produce some stalks that have an extra lobe protruding from their sides, have filaments lacking the 29-kilodalton flagellin, and produce several unusual cell types, including filamentous cells as well as predivisional cells with two stalks and predivisional cells with no stalk at all. We propose that flagellated stalks arise as a consequence of a failure to eject the flagellum at the correct time in the cell cycle and that the extra stalk lobe is due to a second site for the initiation of stalk biogenesis. Thus, a step in the pathway that establishes the characteristic asymmetry of the C. crescentus cell appears to be disrupted in flbT mutants. We have also identified a new structural feature at the flagellated pole and the tip of the stalk: the 10-nm polar particle. The polar particles appear as a cluster of approximately 1 to 10 stain-excluding rings, visible in electron micrographs of negatively stained wild-type cells. This structure is absent at the flagellar pole but not in the stalks of flbT mutant predivisional cells.

Bacteria↗

PubMed1989

The organization of the Caulobacter crescentus flagellar filament.

The structural organization of the flagellar filament of Caulobacter crescentus, as revealed by immunoelectron microscopy, shows five antigenically distinct regions within the hook-filament complex. The first region is the hook. The second region is adjacent to the hook and is approximately 10 nm in length. On the basis of its location in the hook-filament complex, this region may contain hook-associated proteins. Next to this is the third region, which is approximately 60 nm in length. Antibody decoration experiments using mutant strains with deletions of the structural gene for the 29 x 10(3) Mr flagellin (flgJ) showed that the presence of this region is correlated with the expression of the 29 x 10(3) Mr flagellin gene. The next region (region IV), of length approximately 1 to 2 microns, appears to contain the 27.5 x 10(3) Mr flagellin, but at its distal end includes, in gradually increasing amounts, the 25 x 10(3) Mr flagellin. The rest of the filament (region V) is made up predominantly, if not completely, of the 25 x 10(3) Mr flagellin. Except for the hook, there are no morphological features that would otherwise distinguish these regions. A functional flagellum, having the wild-type length and morphology, is assembled by mutant strains deficient in the 29 x 10(3) Mr flagellin and 27.5 x 10(3) Mr flagellin.

Antibodies, Bacterial↗