Construction of a cloning site near one end of Tn917 into which foreign DNA may be inserted without affecting transposition in Bacillus subtilis or expression of the transposon-borne erm gene

Cloning, sequencing and expression of the gene encoding the extracellular neutral protease, vibriolysin, of Vibrio proteolyticus

The gene (nprV), encoding the extracellular neutral protease, vibriolysin (NprV), of the Gram- marine microorganism, Vibrio proteolyticus, was isolated from a V. proteolyticus DNA library constructed in Escherichia coli. The recombinant E. coli produced a protease that co-migrated with purified neutral protease from V. proteolyticus on non-denaturing polyacrylamide gels, and that demonstrated enzymatic specificity towards the neutral protease substrate N-[3-(2-furyl)acryloyl]-L-alanylphenylalanine amide. The nucleotide (nt) sequence of the cloned nprV gene revealed an open reading frame encoding 609 amino acids (aa) including a putative signal peptide sequence followed by a long 'pro' sequence consisting of 172 aa. The N-terminal aa sequence of NprV purified from cultures of V. proteolyticus, identified the beginning of the mature protein within the aa sequence deduced from the nt sequence. Comparative analysis of mature NprV to the sequences of the neutral proteases from Bacillus thermoproteolyticus (thermolysin) and Bacillus stearothermophilus identified extensive regions of conserved aa homology, particularly with respect to active-site residues, zinc-binding residues, and calcium-binding sites. NprV was overproduced in Bacillus subtilis by placing the DNA encoding the 'pro' and mature enzyme downstream from a Bacillus promoter and signal sequence.

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.

Localization of a new promoter, P5, in the sigA operon of Bacillus subtilis and its regulation in some spo mutant strains

The sigA operon of Bacillus subtilis is transcribed from at least two SigA and two SigH promoters. Primer extension and promoter probe analyses have localized a fifth promoter, P5, that is active only at later sporulation stages (T3 to T5). Mutations in the genes for the sigma factors SigG, SigK, SigH, and SigE do not block transcription from P5. The expression from P5 is blocked or severely reduced in spo0A, spo0B, spo0E, and spo0K mutants.

Cloning and characterization of the gene for an additional extracellular serine protease of Bacillus subtilis

We have purified a minor extracellular serine protease from a strain of Bacillus subtilis bearing null mutations in five extracellular protease genes: apr, npr, epr, bpr, and mpr (A. Sloma, C. Rudolph, G. Rufo, Jr., B. Sullivan, K. Theriault, D. Ally, and J. Pero, J. Bacteriol. 172:1024-1029, 1990). During purification, this novel protease (Vpr) was found bound in a complex in the void volume after gel filtration chromatography. The amino-terminal sequence of the purified protein was determined, and an oligonucleotide probe was constructed on the basis of the amino acid sequence. This probe was used to clone the structural gene (vpr) for this protease. The gene encodes a primary product of 806 amino acids. The amino acid sequence of the mature protein was preceded by a signal sequence of approximately 28 amino acids and a prosequence of approximately 132 amino acids. The mature protein has a predicted molecular weight of 68,197; however, the isolated protein has an apparent molecular weight of 28,500, suggesting that Vpr undergoes C-terminal processing or proteolysis. The vpr gene maps in the ctrA-sacA-epr region of the chromosome and is not required for growth or sporulation.

Gene encoding two alkali-soluble components of the spore coat from Bacillus subtilis

We report the cloning and characterization of a gene called cotF from Bacillus subtilis that encodes alkali-soluble polypeptides of 5 and 8 kDa that are components of the spore coat. The 5- and 8-kDa polypeptides are generated by proteolytic cleavage of the primary product of the cotF gene, which is 160 codons in length and is capable of encoding a polypeptide of 19 kDa. Amino acid sequence analysis indicates that the 5-kDa species is derived from the NH2-terminal portion of the primary gene product and that the 8-kDa species is derived from the COOH-terminal portion. A mutant bearing an in vitro-constructed cotF null mutation produced normal-looking spores that contained an apparently complete set of coat proteins except for the absence of the 5- and 8-kDa polypeptides. The map position of cotF is 349 degrees. Transcription of cotF commenced coincidently (during h 6 of sporulation) with genes known to be under the control of sporulation transcription factor sigma kappa.

Processing of the mother-cell sigma factor, sigma K, may depend on events occurring in the forespore during Bacillus subtilis development

During sporulation of the Gram-positive bacterium Bacillus subtilis, transcription of genes encoding spore coat proteins in the mother-cell compartment of the sporangium is controlled by RNA polymerase containing the sigma subunit called sigma K. Based on comparison of the N-terminal amino acid sequence of sigma K with the nucleotide sequence of the gene encoding sigma K (sigK), the primary product of sigK was inferred to be a pro-protein (pro-sigma K) with 20 extra amino acids at the N terminus. Using antibodies generated against pro-sigma K, we have detected pro-sigma K beginning at the third hour of sporulation and sigma K beginning about 1 hr later. Even when pro-sigma K is expressed artificially during growth and throughout sporulation, sigma K appears at the normal time and expression of a sigma K-controlled gene occurs normally. These results suggest that pro-sigma K is an inactive precursor that is proteolytically processed to active sigma K in a developmentally regulated fashion. Mutations that block forespore gene expression block accumulation of sigma K but not accumulation of pro-sigma K, suggesting that pro-sigma K processing is a regulatory device that couples the programs of gene expression in the two compartments of the sporangium. We propose that this regulatory device ensures completion of forespore morphogenesis prior to the synthesis in the mother-cell of spore coat proteins that will encase the forespore.

In vivo genetic systems in lactic acid bacteria

A review of in vivo genetic systems covers the key features of transduction and conjugation but emphasises the intramolecular and intermolecular DNA interactions that are often associated with these processes. As well as the transfer of many lactose plasmids, conjugal transfer of nisin genes and the use of conjugation to construct bacteriophage-resistant dairy starter cultures are discussed. The discovery and characterization of insertion sequences in Lactobacillus and Lactococcus and the exploitation of heterologous conjugation and transposition systems in the lactic acid bacteria are described.

Insertional mutagenesis of Listeria monocytogenes with a novel Tn917 derivative that allows direct cloning of DNA flanking transposon insertions

To carry out efficient insertional mutagenesis in Listeria monocytogenes and to facilitate the characterization of disrupted genes, two novel derivatives of Tn917 were constructed, Tn917-LTV1 and Tn917-LTV3. The derivatives (i) transpose at a significantly elevated frequency, (ii) generate transcriptional lacZ fusions when inserted into a chromosomal gene in the appropriate orientation, and (iii) allow the rapid cloning in Escherichia coli of chromosomal DNA flanking transposon insertions. The rapid cloning of DNA flanking insertions is possible because the transposon derivatives carry ColE1 replication functions, a cluster of polylinker cloning sites, and antibiotic resistance genes selectable in E. coli (bla in the case of Tn917-LTV1; neo and ble in the case of Tn917-LTV3). The enhanced transposition frequency of Tn917-LTV1 and Tn917-LTV3 (about 100-fold in Bacillus subtilis) is believed to be due to the fortuitous placement of vector-derived promoters upstream from the Tn917 transposase gene. In L. monocytogenes, Tn917-LTV3 transposed at a frequency of 8 x 10(-4) when introduced on a pE194Ts-derived vector and generated at least eight different auxotrophic mutations. Two nonhemolytic insertion mutants of L. monocytogenes were isolated, and DNA flanking the transposon insertions was cloned directly into E. coli, making use of the ColE1 rep functions and neo gene carried by Tn917-LTV3. Both insertions were shown to be within hlyA, the L. monocytogenes hemolysin structural gene. Although Tn917-LTV1 and Tn917-LTV3 were constructed specifically for genetic analysis of L. monocytogenes, their enhanced transposition frequency and convenience for cloning of DNA adjacent to sites of insertions make them the transposon derivatives of choice for insertional mutagenesis in any gram-positive bacteria that support replication of pE194Ts.

Cascade regulation of spore coat gene expression in Bacillus subtilis

Endospores of the Gram-positive bacterium Bacillus subtilis are encased in a tough protein shell known as the coat. The coat is composed of a dozen or more different structural proteins. We report the identification of and studies on the regulation of promoters governing the expression of coat protein (cot) genes designated B to E encoding polypeptides of 59, 12, 11 and 24 kDa, respectively. We show that transcription of genes B, C and D is governed by single promoters and that transcription of gene E is governed by tandem promoters designated P1 and P2. In extension of recent work on the transcription of cot gene A and the mother-cell regulatory genes gerE, sigK and spoIIID, we show that genes involved in coat formation are turned on in a regulatory cascade of at least four co-ordinately controlled gene sets. The cascade consists of: cotE as transcribed from its P1 promoter and spoIIID, which are turned on during hours three to four of sporulation; cotE as transcribed from its P2 promoter and sigK, which are turned on during hour five by the appearance of the product (a small DNA-binding protein) of spoIIID; cotA, cotD and gerE, which are turned on during hours five to six by the appearance of the product (sigma factor sigma K) of sigK; and cotB and cotC, which are turned on during hour seven by the appearance of the product (an inferred DNA-binding protein) of gerE. The cascade is hierarchical in that the first three gene sets each contain the regulatory gene that turns on the expression of the next gene set in the pathway. We also show that the level of expression of a member (cotC) of the terminal class of gene expression is strongly influenced by medium and that this effect directly or indirectly depends on the product of sporulation gene spoIV A.

Transcriptional organization of a cloned chemotaxis locus of Bacillus subtilis

A cloned chemotaxis operon has been characterized. Thirteen representative che mutations from different complementation groups were localized on the physical map by recombination experiments. The use of integration plasmids established that at least 10 of these complementation groups within this locus are cotranscribed. An additional three complementation groups may form part of the same transcript. The direction of transcription and the time of expression were determined from chromosomal che-lacZ gene fusions. The promoter was cloned and localized to a 3-kilobase fragment. Expression of beta-galactosidase from this promoter was observed primarily during the logarithmic phase of growth. Three-factor PBS1 cotransduction experiments were performed to order the che locus with respect to adjacent markers. The cheF141 mutation is 70 to 80% linked to pyrD1. This linkage is different from that reported previously (G. W. Ordal, D. O. Nettleton, and J. A. Hoch, J. Bacteriol. 154:1088-1097, 1983). The cheM127 mutation is 57% linked by transformation to spcB3. The gene order determined from all crosses is pyrD-cheF-cheM-spcB.

Bacillopeptidase F of Bacillus subtilis: purification of the protein and cloning of the gene

We have purified a minor extracellular serine protease from Bacillus subtilis. Characterization of this enzyme indicated that it was most likely the previously reported enzyme bacillopeptidase F. The amino-terminal sequence of the purified protein was determined, and a "guess-mer" oligonucleotide hybridization probe was constructed on the basis of that sequence. This probe was used to identify and clone the structural gene (bpr) for bacillopeptidase F. The deduced amino acid sequence for the mature protein (496 amino acids) was preceded by a putative signal sequence of 30 residues and a putative propeptide region of 164 amino acids. The bpr gene mapped near pyrD on the chromosome and was not required for growth or sporulation.

Gene encoding a novel extracellular metalloprotease in Bacillus subtilis

The gene for a novel extracellular metalloprotease was cloned, and its nucleotide sequence was determined. The gene (mpr) encodes a primary product of 313 amino acids that has little similarity to other known Bacillus proteases. The amino acid sequence of the mature protease was preceded by a signal sequence of approximately 34 amino acids and a pro sequence of 58 amino acids. Four cysteine residues were found in the deduced amino acid sequence of the mature protein, indicating the possible presence of disulfide bonds. The mpr gene mapped in the cysA-aroI region of the chromosome and was not required for growth or sporulation.

Identification and characterization of genes controlled by the sporulation-regulatory gene spo0H in Bacillus subtilis

We describe a general strategy for the identification of genes that are controlled by a specific regulatory factor in vivo and the use of this strategy to identify genes in Bacillus subtilis that are controlled by spo0H, a regulatory gene required for the initiation of sporulation. The general strategy makes use of a cloned regulatory gene fused to an inducible promoter to control expression of the regulatory gene and random gene fusions to a reporter gene to monitor expression in the presence and absence of the regulatory gene product. spo0H encodes a sigma factor of RNA polymerase, sigma H, and is required for the extensive reprograming of gene expression during the transition from growth to stationary phase and during the initiation of sporulation. We identified 18 genes that are controlled by sigma H (csh genes) in vivo by monitoring expression of random gene fusions to lacZ, made by insertion mutagenesis with the transposon Tn917lac, in the presence and absence of sigma H. These genes had lower levels of expression in the absence of sigma H than in the presence of sigma H. Patterns of expression of the csh genes during growth and sporulation in wild-type and spo0H mutant cells indicated that other regulatory factors are probably involved in controlling expression of some of these genes. Three of the csh::Tn917lac insertion mutations caused noticeable phenotypes. One caused a defect in vegetative growth, but only in combination with a spo0H mutation. Two others caused a partial defect in sporulation. One of these also caused a defect in the development of genetic competence. Detailed characterization of some of the csh genes and their regulatory regions should help define the role of spo0H in the regulation of gene expression during the transition from growth to stationary phase and during the initiation of sporulation.

Regulatory studies on the promoter for a gene governing synthesis and assembly of the spore coat in Bacillus subtilis

gerE is a regulatory gene of Bacillus subtilis that governs the synthesis and assembly of the spore coat and is required for the production of spores that are lysozyme-resistant and germination-proficient. We report the identification of the promoter for gerE and studies on the regulation of its expression. We show that gerE is switched on at the fourth hour of sporulation (stage-V) and that this expression is restricted to the mother-cell chamber of the sporangium. Dependency studies in which the level of gerE expression was measured in 36 different developmental mutants indicate that efficient expression of gerE requires the products of almost all spo0-IV genes tested as well as certain spoV genes. On the basis of its time of induction, compartmentalization of expression and pattern of dependence on other spo genes, gerE is inferred to be regulated co-ordinately with the previously studied spore coat protein gene cotA. gerE and cotA may be members of a developmental regulon of genes whose products are involved in the assembly of the spore coat.

Construction, transfer and properties of a novel temperature-sensitive integrable plasmid for genomic analysis of Staphylococcus aureus

As an alternative approach to genetic transfer and analysis, a novel integrable plasmid system was developed that should prove useful for mapping and cloning various genes in Staphylococcus aureus and other Gram-positive bacteria. The use of a restriction-deficient recipient strain and an improved protocol for protoplast plasmid transformation facilitated direct cloning of a recombinant plasmid (pPQ126) in S. aureus NCTC 8325-4. Plasmid pPQ126 (13.6 kb) is a novel, temperature-sensitive integrable plasmid containing genes encoding resistance to erythromycin and chloramphenicol (from plasmid pTV1ts), and resistance to gentamicin (from transposon Tn4001). When introduced into an appropriate recipient strain at the permissive temperature (30 degrees C), pPQ126 replicates autonomously. Integration of pPQ126 is directed into homologous chromosomal target sequences (chromosomal insertions of Tn551 or Tn4001) by growing a population of cells containing autonomous pPQ126 in the presence of gentamicin, erythromycin, and chloramphenicol at 39 degrees C (nonpermissive temperature). Elevated temperature both selects for and maintains pPQ126 as an integrated replicon. Integration of pPQ126 occurs at significantly reduced frequency in a recombination-deficient host, and does not occur in the absence of host chromosomal homology. Integrated pPQ126 excises from the chromosome under permissive conditions (30 degrees C), and excision results in derivatives of pPQ126 that harbour DNA of chromosomal origin.

A new cloning system for Bacillus subtilis comprising elements of phage, plasmid and transposon vectors

A new cloning system for Bacillus subtilis was devised which makes use of a combination of Tn917-containing phage SP beta derivatives and Tn917-containing Escherichia coli-B. subtilis shuttle plasmids. This system allows the initial cloning of genes in single copy, via 'prophage transformation', with a selection for complementation of mutational defects in B. subtilis hosts and permits subsequent transfer of the cloned material by homologous recombination to low-copy and high-copy vectors that replicate in both B. subtilis and E. coli. Because cloned sequences are adjacent to pB322-derived DNA in the recombinant phages, inserts can also be 'rescued' directly from the phage DNA after digestion with appropriate restriction enzymes, circularization of the fragments by ligation and transformation of an E. coli recipient. Two genomic libraries of B. subtilis chromosomal Sau3A-generated partial-digest fragments in the size ranges of 5-8 kb and 8-10 kb were constructed and screened for the complementation of mutations aroI906, cysA14, dal-1, glyB133, metC3, purA16, purB33, thrA5, trpC2 and recE4. In all cases, specialized transducing phages carrying inserts that complemented the selected markers were recovered. Inserts complementing the dal-1 and trpC2 mutations could be transferred from recombinant phages to Tn917-containing plasmids by homologous recombination without in vitro subcloning. Another insert complementing the purB33 mutation was rescued directly into E. coli from a recombinant phage DNA.

Gene encoding a minor extracellular protease in Bacillus subtilis

The gene for a minor, extracellular protease has been identified in Bacillus subtilis. The gene (epr) encoded a primary product of 645 amino acids that was partially homologous to both subtilisin (Apr) and the major internal serine protease (ISP-1) of B. subtilis. Deletion analysis indicated that the C-terminal 240 amino acids of Epr were not necessary for activity. This C-terminal region exhibited several unusual features, including a high abundance of lysine residues and the presence of a partially homologous sequence of 44 amino acids that was directly repeated five times. The epr gene mapped near sacA and was not required for growth or sporulation.

Identification of the protein encoded by rodC, a cell division gene from Bacillus subtilis

The rodC1 mutation of Bacillus subtilis is a temperature-sensitive marker which affects the orientation of the plane of cell division. We have cloned the rodC gene and have localized the site of the rodC1 lesion. To identify the rodC gene product, we have subjected several plasmid clones containing B. subtilis chromosomal DNA from the rodC region to maxicell analysis in Escherichia coli. A 68 kiloDalton protein has been identified as the rodC gene product. This is the initial cloning of a cell division gene and the identification of its product from B. subtilis. The rodC gene has also been implicated as being directly associated with the synthesis of glycerol teichoic acid.

The promoter for a sporulation gene in the spoIVC locus of Bacillus subtilis and its use in studies of temporal and spatial control of gene expression

We have identified the transcription start site and regulatory region governing the expression of a sporulation gene in the spoIVC locus of Bacillus subtilis. Efficient expression and developmental regulation of this gene was controlled from a promoter region that extended no more than 110 base pairs upstream and no more than 4 base pairs downstream from the start site of transcription, on which basis we infer that spoIVC is regulated at the level of transcription initiation. Using a transcriptional fusion of the spoIVC gene to the lacZ gene of Escherichia coli, we found that spoIVC expression was turned on at the third to fourth hour of sporulation (at about the developmental stage [IV] that its products are required in spore formation) and that this transcription was largely restricted to the mother cell chamber of the sporangium. Mutations in many different spo genes (causing blocks at stages 0 to V) were found to influence (negatively and positively) the level of spoIVC expression. Our results distinguish the mode of spoIVC regulation from that of previously studied sporulation genes and indicate that it is representative of a new regulon of mother cell-specific gene expression.

Identification of the promoter for a spore coat protein gene in Bacillus subtilis and studies on the regulation of its induction at a late stage of sporulation

The cotA (pig) gene of Bacillus subtilis encodes a 65,000 Mr protein that is a component of the spore coat and is responsible for the brown pigment characteristic of colonies in which cells are undergoing sporulation. To study developmental regulation of the cotA gene, we identified its promoter and studied its transcription in a large number of mutants blocked at various stages of sporulation and germination. Deletion analysis showed that induction and efficient transcription of cotA required DNA sequences extending no more than 55 base pairs (bp) upstream (and no more than 130 bp downstream) from the 5' terminus of cotA mRNA. Transcription from the cotA promoter was found to be switched on at approximately the time (4 to 5 h after the onset of sporulation) of spore coat synthesis and deposition. Strikingly, this transcription was substantially inhibited in almost all asporogenous mutants blocked prior to the developmental stage (V) of spore coat formation. cotA transcription was also impaired in several stage V mutants but not in other stage V mutants or in mutants blocked in germination. The germination mutant gerE caused a several-fold overexpression of cotA. The dependence of cotA expression on so many genes required at early to intermediate stages of sporulation suggests that transcription of this spore coat gene is somehow coupled (directly or through several intervening steps) to a morphological or physiological feature(s) of the developing sporangium.

Bacillus subtilis (natto) plasmid pLS20 mediates interspecies plasmid transfer

The 55-kilobase plasmid, pLS20, of Bacillus subtilis (natto) 3335 promotes transfer of the tetracycline resistance plasmid pBC16 from B. subtilis (natto) to the Bacillus species B. anthracis, B. cereus, B. licheniformis, B. megaterium, B. pumilus, B. subtilis, and B. thuringiensis. Frequency of pBC16 transfer ranged from 2.3 x 10(-6) to 2.8 x 10(-3). Evidence for a plasmid-encoded conjugationlike mechanism of genetic exchange includes (i) pLS20+ strains, but not pLS20- strains, functioned as donors of pBC16; (ii) plasmid transfer was insensitive to the presence of DNase; and (iii) cell-free filtrates of donor cultures did not convert recipient cells to Tcr. Cotransfer of pLS20 and pBC16 in intraspecies matings and in matings with a restriction-deficient B. subtilis strain indicated that pLS20 was self-transmissible. In addition to mobilizing pBC16, pLS20 mediated transfer of the B. subtilis (natto) plasmid pLS19 and the Staphylococcus aureus plasmid pUB110. The fertility plasmid did not carry a selectable marker. To facilitate direct selection for pLS20 transfer, plasmid derivatives which carried the erythromycin resistance transposon Tn917 were generated. Development of this method of genetic exchange will facilitate the introduction of plasmid DNA into nontransformable species by use of transformable fertile B. subtilis or B. subtilis (natto) strains as intermediates.

Conjugal transfer of transposon Tn916 from Streptococcus faecalis to Mycoplasma hominis

Transposon Tn916 was transferred from Streptococcus faecalis to Mycoplasma hominis by a mating process resembling conjugation with a frequency of 10(-6) to 10(-7). Tn916 was inserted into the mycoplasmal chromosome in single and multiple copies.

The nucleotide sequence and gene organization of the gerA spore germination operon of Bacillus subtilis 168

The nucleotide sequence of the second and third genes in the Bacillus subtilis spore germination locus, gerA, has been determined and the amino acid (aa) sequence was derived. Two open reading frames (ORFs), corresponding to genes II and III, encode 364-aa residue and 373-aa residue polypeptides, respectively. The gene II product, Mr 41,257, would contain long stretches of hydrophobic aa residues and may be a membrane protein; the gene III product, Mr 42,363, is relatively hydrophilic but possesses an apparent signal peptide for transfer across, and perhaps localisation on, a membrane. The ORFs for genes I and II overlap by eleven codons and the termination codon of gene II overlaps the initiation codon of gene III. Insertional inactivation experiments using integrational plasmids have indicated that the gerA locus is a single transcriptional unit. The expression of the gerA genes has been studied using a lacZ transcriptional fusion; they constitute a developmentally regulated operon.

Transposition of Tn917 in Bacillus megaterium

Transposon Tn917, carried on plasmid pTV1, was introduced into Bacillus megaterium and transposed efficiently and apparently randomly. Insertional mutations included at least eight different auxotrophic loci, two carbon source loci, and sporulation loci. One trp::Tn917 mutation was further verified as an insertion by both reversion and transduction.

Construction and properties of Tn917-lac, a transposon derivative that mediates transcriptional gene fusions in Bacillus subtilis

A derivative of Tn917 was constructed, referred to as Tn917-lac, which is capable of generating fusions that connect the transcripts of Bacillus subtilis chromosomal genes to the coding sequence of the lacZ gene of Escherichia coli. Two independent insertions of Tn917-lac into the gltA gene and one insertion into the trpE gene (in the trpEDCFBA operon) of B. subtilis were studied in detail, and the results confirmed that Tn917-lac-mediated transcriptional fusions produce levels of beta-galactosidase that reflect accurately the regulated expression of interrupted genes. To facilitate these studies, a procedure was developed that permits the analysis of Tn917-lac-mediated fusions in partial diploids where insertional mutations are complemented by an intact copy of the interrupted genes. Tn917 is known to function efficiently in bacteria representing three quite different Gram-positive genera (Streptococcus, Bacillus, and Staphylococcus) and is known to display a relatively high degree of randomness in its insertions into bacterial genomes, making it likely that Tn917-lac will be useful for the identification and study of many kinds of regulated genes in a wide range of Gram-positive species.

Complete nucleotide sequence of macrolide-lincosamide-streptogramin B-resistance transposon Tn917 in Streptococcus faecalis

Streptococcus faecalis transposon Tn917 was cloned in Escherichia coli on plasmid vector pBR325. The erythromycin resistance determinant of Tn917 was not expressed in the E. coli background. The nucleotide sequence of Tn917 was determined and found to be 5,257 base pairs in length. Six open reading frames (ORFs) were identified and designated 1 through 6 (5' to 3'); all were on the same DNA strand. A region exhibiting strong homology with known promoters was identified upstream from ORF1. ORFs 1 to 3 were virtually identical to the previously sequenced erythromycin resistance determinant on Streptococcus sanguis plasmid pAM77. At the 3' point, where the homology between Tn917 and pAM77 ends, was a 20-base-pair region about 80% homologous with a component of the res site of Tn3. The amino acid sequence of ORF4 showed homology with other site-specific recombination enzymes, including approximately 30% homology with the resolvase of Tn3. Contained within Tn917 was a directly oriented 73-base-pair duplication of the left terminus. The Tn917 sequence revealed that antibiotic-enhanced transposition might be due to extension of transcription from the resistance-related genes (in ORFs 1 to 3) into transposition genes (in ORFs 4 to 6). Transcription analyses resulted in data consistent with this interpretation.

New Ways to Study Developmental Genes in Spore-Forming Bacteria

The regulated activation of numerous sets of genes in multiple chromosomal locations is a hallmark of cellular differentiation in both eukaryotes and prokaryotes. Certain species of bacteria that experience complex developmental cycles are especially attractive as systems in which to study the mechanisms of this kind of gene regulation because they are highly amenable to both biochemical and genetic approaches. Bacillus subtilis, which undergoes extensive cellular differentiation when it sporulates, is one such system. Many new methods are now available in this Gram-positive species for identifying, manipulating, and studying the regulation of genes involved in spore formation, including the use of transposable genetic elements that create gene fusions in vivo as an automatic consequence of insertions into genes.

A physical and functional analysis of Tn917, a Streptococcus transposon in the Tn3 family that functions in Bacillus

The erythromycin-resistance (Emr)-conferring transposon Tn917, first isolated in the genus Streptococcus, has in previous work been shown to function efficiently in the spore-forming species Bacillus subtilis, where it has been developed as a tool for identifying and studying sporulation genes. In the present work, a physical analysis of Tn917 was undertaken, including detailed restriction mapping, chemical DNA sequencing, heteroduplex studies, and Southern hybridization analysis, as a first step in understanding the genetic organization of this useful insertion element. The location and transcriptional orientation of the transposon-borne erm gene (the gene responsible for the Emr phenotype) have been determined, and a partial sequence of DNA 5' to the coding sequence of this gene indicates that its inducibility is probably the result of "translational attenuation," a mechanism known to be responsible for the regulation of at least two other gram-positive erm genes. Restriction mapping and heteroduplex analysis have revealed extensive homology between Tn917 and the Staphylococcus transposon Tn551, throughout virtually their entire lengths, and DNA sequencing studies have revealed a remarkably high degree of sequence correspondence within the terminal inverted repeats of Tn917, Tn551 and the gram-negative transposon Tn3. Tn917 was also shown to generate a 5-bp duplication upon insertion, as do Tn3 and Tn551 (and all of the other Tn3-related elements studied thus far), strengthening the conclusion that these three transposons are members of a highly dispersed family of related insertion elements which populate both gram-positive and gram-negative genera.

A novel method for the rapid cloning in Escherichia coli of Bacillus subtilis chromosomal DNA adjacent to Tn917 insertions

A rapid and general procedure has been devised for the pBR322-mediated cloning in Escherichia coli of Bacillus subtilis chromosomal DNA extending in a specified direction from any Tn917 insertion. Derivatives of Tn917 have been constructed that contain a pBR322-derived replicon, together with a chloramphenicol-resistance (Cmr) gene of Gram-positive origin (selectable in B. subtilis), inserted by ligation in two orientations into a SalI restriction site located near the center of the transposon. When linearized plasmid DNA carrying such derivatives was used to transform to Cmr B. subtilis bacteria already containing a chromosomal insertion of Tn917, the pBR322 sequences efficiently became integrated into the chromosomal copy of the transposon by homologous recombination. It was then possible to clone chromosomal sequences adjacent to either transposon insertion junction into E. coli, using a selection for ampicillin-resistance, by transforming CaCl2-treated cells with small amounts of insert-containing DNA that had been digested with various restriction enzymes and then ligated at a dilute concentration. Because pBR322 sequences may be inserted by recombination in either orientation with respect to the transposon arms, a single restriction enzyme (such as EcoRI or SphI) that has a unique recognition site in pBR322 DNA may be used to separately clone chromosomal DNA extending in either direction from the site of any transposon insertion. A family of clones generated from the region of an insertional spo mutation (spoIIH::Tn917) was used in Southern hybridization experiments to verify that cloned material isolated with this procedure accurately reflected the arrangement of sequences present in the chromosome. Strategies are discussed for taking advantage of certain properties inherent in the structure of clones generated in this way to facilitate the identification and study of promoters of insertionally mutated genes.