R factor proteins synthesized in Escherichia coli minicells: incorporation studies with different R factors and detection of deoxyribonucleic acid-binding proteins

A novel determinant (comA) essential for natural transformation competence in Neisseria gonorrhoeae and the effect of a comA defect on pilin variation

A novel genetic determinant (comA) has been identified and found to be required for the transformation of piliated Neisseria gonorrhoeae. Mutants in comA of strain MS11 grow normally and are DNA-uptake proficient but blocked in the translocation of DNA into the cytoplasm. Here we show by site-specific mutagenesis and genetic complementation that only one of two open reading frames identified in comA is essential for competence: it encodes a protein (ComA) with a predicted size of 74 kDa. The comA gene maps upstream of the iga locus and is transcribed in the opposite orientation, probably under the control of a putative sigma 54-type promoter. While DNA probes specific for the N. gonorrhoeae iga locus reveal only a little cross-reactivity with commensal Neisseria species, the neighbouring comA gene appears to be present in most of them. ComA fusion proteins were obtained by in vitro translation. The synthesized gene products migrated atypically in SDS gels indicating its strong hydrophobicity. Several transmembrane alpha-helices were predicted from the amino acid sequence of ComA which, in the context of an observed sequence similarity with other inner membrane proteins, suggests a location for the protein in the inner membrane. Using piliated and non-piliated comA mutants the consequences of transformation deficiency on pilin phase variation were assessed. We show that the comA defect affects some but not all types of DNA rearrangements associated with pilE variation. The results are in agreement with previous observations supporting the notion that multiple recombination pathways contribute to the variability of pilE.

Cloning and genetic characterization of a Helicobacter pylori flagellin gene

Helicobacter pylori produces polar sheathed flagella, which are believed to be essential for the bacterial colonization of the human gastric mucosa. Here we report on the cloning and genetic characterization of a H. pylori gene encoding the subunit of the flagellar filament, the flagellin. Screening of a genomic library of H. pylori with an oligonucleotide probe derived from the N-terminal amino acid sequence of purified flagellin resulted in a recombinant plasmid clone carrying the flagellin-encoding gene flaA on a 9.3 kb Bg/II fragment. The nucleotide sequence of flaA revealed an open reading frame of 1530 nucleotides, encoding a protein with a predicted molecular mass of 53.2 kDa, which is similar in size with the purified flagellin protein in SDS-polyacrylamide gel electrophoresis. Sequence alignment of H. pylori flagellin (FlaA) with other bacterial flagellins demonstrates a high degree of similarity in the amino-terminal and carboxy-terminal regions, including those of the closely related genus Campylobacter (56% overall identity with Campylobacter coli flaA), but little homology in the central domain. Southern hybridizations of chromosomal DNA with flaA-specific probes did not reveal the presence of additional homologous flagellin genes in H. pylori. Sequence analysis of the flaA flanking regions and mapping of the flaA mRNA start site by a primer extension experiment indicated that transcription of the gene is under the control of a sigma 28-specific promoter sequence in H. pylori. The region upstream of the flaA promoter is subject to local DNA modification, resulting in the masking of two out of three closely linked HindIII restriction sites in the chromosome of strain 898-1. Escherichia coli strains harbouring the recombinant plasmid did not produce full-length flagellin and data obtained with FlaA fusion proteins using an E. coli plasmid expression system suggest that a distinct nucleotide sequence in the gene interferes with productive translation of this protein in E. coli.

The sequences of genes bordering oriT in the enterotoxin plasmid P307: comparison with the sequences of plasmids F and R1

The nucleotide sequences of the enterotoxin plasmid P307 transfer genes traM, finP, traJ, traY, and gene 19 were determined. Gene 19 is highly conserved; its product is very similar to that coded by the F and R1 plasmids. The TraM protein is similar in P307 and in F; the R1 sequence shows differences in the 40 N-terminal amino acids. The traJ product is very different in P307, F, and R1. The traY gene from P307, which in F is almost twice as long, is similar in size to that from R1. The finP RNA shows a high degree of homology with that from R1 and F, except for the two loop regions where base changes were observed. The genes coding for proteins, except traY, could be expressed in minicell- and T7 promoter-driven expression systems, whereas traJ and gene 19 could be expressed only in the latter system.

envM genes of Salmonella typhimurium and Escherichia coli

Conjugation and bacteriophage P1 transduction experiments in Escherichia coli showed that resistance to the antibacterial compound diazaborine is caused by an allelic form of the envM gene. The envM gene from Salmonella typhimurium was cloned and sequenced. It codes for a 27,765-dalton protein. The plasmids carrying this DNA complemented a conditionally lethal envM mutant of E. coli. Recombinant plasmids containing gene envM from a diazaborine-resistant S. typhimurium strain conferred the drug resistance phenotype to susceptible E. coli cells. A guanine-to-adenine exchange in the envM gene changing a Gly codon to a Ser codon was shown to be responsible for the resistance character. Upstream of envM a small gene coding for a 10,445-dalton protein was identified. Incubating a temperature-sensitive E. coli envM mutant at the nonpermissive temperature caused effects on the cells similar to those caused by treatment with diazaborine, i.e., inhibition of fatty acid, phospholipid, and lipopolysaccharide biosynthesis, induction of a 28,000-dalton inner membrane protein, and change in the ratio of the porins OmpC and OmpF.

Molecular cloning and nucleotide sequence of the gene for Escherichia coli leucyl-tRNA synthetase

The gene for Escherichia coli leucyl-tRNA synthetase leuS has been cloned by complementation of a leuS temperature sensitive mutant KL231 with an E.coli gene bank DNA. The resulting clones overexpress leucyl-tRNA synthetase (LeuRS) by a factor greater than 50. The DNA sequence of the complete coding regions was determined. The derived N-terminal protein sequence of LeuRS was confirmed by independent protein sequencing of the first 8 aminoacids. Sequence comparison of the LeuRS sequence with all aminoacyl-tRNA synthetase sequences available reveal a significant homology with the valyl-, isoleucyl- and methionyl-enzyme indicating that the genes of these enzymes could have derived from a common ancestor. Sequence comparison with the gene product of the yeast nuclear NAM2-1 suppressor allele curing mitochondrial RNA maturation deficiency reveals about 30% homology.

Aberrant regulation of synthesis and degradation of viral proteins in coliphage lambda-infected UV-irradiated cells and in minicells

The patterns of bacteriophage lambda proteins synthesized in UV-irradiated Escherichia coli cells and in anucleate minicells are significantly different; both systems exhibit aberrations of regulation in lambda gene expression. In unirradiated cells or cells irradiated with low UV doses (less than 600 J/m2), regulation of lambda protein synthesis is controlled by the regulatory proteins CI, N, CII, CIII, Cro, and Q. As the UV dose increases, activation of transcription of the cI, rexA, and int genes by CII and CIII proteins fails to occur and early protein synthesis, normally inhibited by the action of Cro, continues. After high UV doses (greater than 2,000 J/m2), late lambda protein synthesis does not occur. Progression through the sequence of regulatory steps in lambda gene expression is slower in infected minicells. In minicells, there is no detectable cII- and cIII-dependent synthesis of CI, RexA, or Int proteins and inhibition of early protein synthesis by Cro activity is always incomplete. The synthesis of early b region proteins is not subject to control by CI, N, or Cro proteins, and evidence is presented suggesting that, in minicells, transcription of the early b region is initiated at a promoter(s) within the b region. Proteolytic cleavage of the regulatory proteins O and N and of the capsid proteins C, B, and Nu3 is much reduced in infected minicells. Exposure of minicells to very high UV doses before infection does not completely inhibit late lambda protein synthesis.

T-even-type bacteriophages use an adhesin for recognition of cellular receptors

Protein 38 of the Escherichia coli phage T4 is thought to be required catalytically for the assembly of the long tail fibers of this phage. It is shown that this protein of phage T2 and the T-even-type phage K3 and Ox2 act differently. It was found that NH2-terminal fragments of the protein, expressed from cloned fragments of gene 38 of phage K3, bind to gene 38 amber mutants of phage T2. Such phage or T2 gene 38 amber mutants, grown on a non-permissive host, possess a complete set of six tail fibers but are non-infectious. Both types of non-infectious phage could be repaired by incubation with an extract of cells harboring a cloned gene 38 of a host range mutant of phage K3, K3hx. The repaired phages had the host range of K3hx and not of T2. Immuno-electron microscopy showed that protein 38 is located at the free ends of the long tail fibers of phages T2, K3 and Ox2. The protein serves the recognition of the cellular receptor, i.e. it acts as an adhesin.

Cloning and characterization of the gene for Escherichia coli seryl-tRNA synthetase

Seryl-tRNA synthetase is the gene product of the serS locus in Escherichia coli. Its gene has been cloned by complementation of a serS temperature sensitive mutant K28 with an E. coli gene bank DNA. The resulting clones overexpress seryl-tRNA synthetase by a factor greater than 50 and more than 6% of the total cellular protein corresponds to the enzyme. The DNA sequence of the complete coding region and the 5'- and 3' untranslated regions was determined. Protein sequence comparison of SerRS with all available aminoacyl-tRNA synthetase sequences revealed some regions of significant homology particularly with the isoleucyl- and phenylalanyl-tRNA synthetases from E. coli.

Cloning and characterization of the gene encoding 3-deoxy-D-manno-octulosonate 8-phosphate synthetase from Escherichia coli

The cloning of the gene for Escherichia coli PL-2 2-keto-3-deoxy-D-manno-octonate 8-phosphate synthetase is reported. Positive transformants showed an increase of approximately three-fold in specific activity of the enzyme both in E. coli and in Salmonella typhimurium as host cells. A subclone containing a 1.5-kilobase PvuII fragment overproduced active enzyme. Minicell experiments that allow the detection of plasmid encoded proteins revealed an insert-coded single protein band of 34 kilodaltons.

The sequences of the traJ gene and the 5' end of the traY gene of the resistance plasmid R1

The traJ gene and the 5' end of the neighbouring traY gene of the resistance plasmid R1 were sequenced. Both structural genes show relatively little homology with the corresponding sequences of the related F plasmid. At the amino acid level sufficient homology is detected to allow an assignment of the two genes in R1. In traJ two methionine codons have to be regarded as potential chain initiation signals. Because of the analogy with the F plasmid sequence the second ATG is believed to be the main translational start site. The traJ gene codes for 228 amino acids. The 5' untranslated region of the traJ gene of R1 is highly homologous to the corresponding sequence in F indicating that it fulfills an important role in regulation. The transcription of the traY-Z operon starts in the structural gene of traJ. The amino terminal part of the TraY protein shows only limited homology with the F factor counterpart. However, the few conserved amino acids are a strong indication that our sequence contains the traY gene of R1.

Nucleotide sequence of an Escherichia coli chromosomal hemolysin

We determined the DNA sequence of an 8,211-base-pair region encompassing the chromosomal hemolysin, molecularly cloned from an O4 serotype strain of Escherichia coli. All four hemolysin cistrons (transcriptional order, C, A, B, and D) were encoded on the same DNA strand, and their predicted molecular masses were, respectively, 19.7, 109.8, 79.9, and 54.6 kilodaltons. The identification of pSF4000-encoded polypeptides in E. coli minicells corroborated the assignment of the predicted polypeptides for hlyC, hlyA, and hlyD. However, based on the minicell results, two polypeptides appeared to be encoded on the hlyB region, one similar in size to the predicted molecular mass of 79.9 kilodaltons, and the other a smaller 46-kilodalton polypeptide. The four hemolysin gene displayed similar codon usage, which is atypical for E. coli. This reflects the low guanine-plus-cytosine content (40.2%) of the hemolysin DNA sequence and suggests the non-E. coli origin of the hemolysin determinant. In vitro-derived deletions of the hemolysin recombinant plasmid pSF4000 indicated that a region between 433 and 301 base pairs upstream of the putative start of hlyC is necessary for hemolysin synthesis. Based on the DNA sequence, a stem-loop transcription terminator-like structure (a 16-base-pair stem followed by seven uridylates) in the mRNA was predicted distal to the C-terminal end of hlyA. A model for the general transcriptional organization of the E. coli hemolysin determinant is presented.

Escherichia coli hemolysin is released extracellularly without cleavage of a signal peptide

A 110-kilodalton polypeptide isolated from cell-free culture supernatants of hemolytic Escherichia coli was shown to be associated with hemolytic activity. The relative amount of the extracellular 110-kilodalton species detected directly reflects the extracellular hemolysin activity associated with Escherichia coli strains harboring different hemolysin recombinant plasmids. The predicted molecular mass of the hemolysin structural gene (hlyA) based on DNA sequence analysis was 109,858 daltons. Amino-terminal amino acid sequence analysis of the 110-kilodalton polypeptide provided direct evidence that it was encoded by hlyA. Based on this information, it was also demonstrated that the HlyA polypeptide was released extracellularly without signal peptidase-like cleavage. An examination of hemolysin-specific polypeptides detected by use of recombinant plasmids in a minicell-producing strain of Escherichia coli was performed. These studies demonstrated how hemolysin-associated 110- and 58-kilodalton polypeptides detected in the minicell background could be misinterpreted as a precursor-product relationship.

Intracistronic complementation of the tetracycline resistance membrane protein of Tn10

The structural gene region for tetracycline resistance on Tn10 consists of two complementation groups, tetA and tetB (M. S. Curiale and S. B. Levy, J. Bacteriol. 151:209-215, 1982). Using a series of deletion mutants, we have determined that the tetA region is 450 to 600 base pairs long and that the tetB region, which is adjacent to tetA, is 600 to 750 base pairs long. Point mutations in either tetA or tetB affected the amount and size of the inducible inner-membrane Tet protein synthesized in Escherichia coli maxicells. Moreover, deletions in these regions led to the synthesis of an appropriately smaller Tet protein. A single tetracycline-inducible RNA of about 1,200 bases was detected that was homologous with the tetracycline resistance structural gene region. These results indicate that the tetA and tetB complementation regions represent two parts of a single gene encoding two domains of the tetracycline resistance protein Tet.

Transcription of plasmid DNA in Escherichia coli minicells

Cellular RNA polymerase in association with plasmid DNA segregates into the minicells of minicell-producing strains. In general, one "plasmid equivalent" of RNA polymerase, reflecting the size of the segregating plasmid DNA and its efficiency of segregation, entered the minicell with the plasmid. The amount of RNA polymerase (measured as the amount of enzyme activity purified from minicells and the rate of RNA synthesis in plasmid-containing minicells), and not the DNA content, appeared to be rate-limiting in plasmid-mediated transcription in minicells. The purified minicell and cellular RNA polymerases showed the same sensitivity to rifampin and streptolydigin; both were associated with sigma factor, although the minicell enzyme appeared to have slightly less than the cellular enzyme. These studies demonstrate that transcription of plasmid DNA in minicells is a function of the efficiency of segregation and the amount of RNA polymerase which enters with the plasmid DNA. Because RNA polymerase is limiting, plasmids with relatively weak promoters for the vector genes should be used when attempting to identify products from inserted foreign DNA.

IgA1 proteases of Haemophilus influenzae: cloning and characterization in Escherichia coli K-12

Haemophilus influenzae is one of several bacterial pathogens known to release IgA1 proteases into the extracellular environment. Each H. influenzae isolate produces one of at least three distinct types of these enzymes that differ in the specific peptide bond they cleave in the hinge region of human IgA1. We have isolated the gene specifying type 1 IgA1 protease from a total genomic library of H. influenzae, subcloned it into plasmid vectors, and introduced these vectors into Escherichia coli K-12. The enzyme synthesized by E. coli was active and had the same specificity as that of the H. influenzae donor. Unlike that of the donor, E. coli protease activity accumulated in the periplasm rather than being transported extracellularly. The position of the protease gene in H. influenzae DNA and its direction of transcription was approximated by deletion mapping. Tn5 insertions, and examination of the polypeptides synthesized by minicells. A 1-kilobase probe excised from the IgA1 protease gene hybridized with DNA restriction fragments of all H. influenzae serogroups but not with DNA of a nonpathogenic H. parainfluenzae species known to be IgA1 protease negative.

traJ independence in expression of traT on F

Studies of F plasmids in the same cell as a transfer-repressed IncFII R plasmid showed a 100 to 1,000-fold decrease in transfer and a 75-fold decrease in surface exclusion, but no detectable change was shown in the amount of TraTp synthesized. Moreover, a mutation in traJ on F which caused a 10(4)-fold reduction in transfer caused only a 3.6-fold decrease in TraTp. These two findings suggest that a significant amount of traT expression on F is independent of traJ. Furthermore, we showed, using immunoprecipitation of TraTp, that normal amounts of this protein could be present in the cell without producing normal levels of surface exclusion.

Characterization of virulence plasmids and plasmid-associated outer membrane proteins in Shigella flexneri, Shigella sonnei, and Escherichia coli

The 140-megadalton plasmids of Shigella flexneri serotypes 1, 3, and 5, in addition to the 120-megadalton plasmid of Shigella sonnei, are associated with virulence. The present study showed that a 140-megadalton plasmid is also associated with virulence in Escherichia coli. When these plasmids were cleaved with EcoRI or BamHI restriction endonucleases, considerable homology was evident in plasmids from S. sonnei strains, whereas only a few common fragments were observed among the S. flexneri and enteroinvasive E. coli plasmids. Nitrocellulose filter hybridization demonstrated that, despite variations in restriction sites, all these plasmids shared a considerable complement of homologous sequences. Minicell-producing strains were obtained by N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis. Transmission electron microscopy of infected HeLa cells showed that minicells from invasive strains retained the invasive phenotype. Sixteen polypeptides were labeled when S. flexneri 5 minicells were incubated with [35S]methionine. Fourteen of these plasmid-coded polypeptides were associated with the outer membrane in invasive strains of S. flexneri 5, and nine polypeptides of similar molecular weight were labeled in the outer membrane of invasive strains of S. flexneri 3, S. sonnei, and E. coli. Seven of the S. flexneri 5 polypeptides were not labeled in a noninvasive strain which had sustained a large deletion in the virulence-associated plasmid, and none were labeled in minicells which no longer harbored this plasmid.

Tn1721-encoded tetracycline resistance: mapping of structural and regulatory genes mediating resistance

The genes encoding inducible tetracycline resistance in Tn1721 were located in a 2.1-kilobase portion of the transposon. Using deletions and insertions, we mapped and characterized two tet genes by their mutant phenotypes. Two tetracycline-inducible polypeptides synthesized in minicells were assigned to the tet genes. The polarity of the tet genes was determined by employing a deletion and a gene fusion which altered the carboxy termini of the polypeptides. The gene responsible for resistance (tetA) encompasses 1,250 base pairs and encodes a membrane-bound protein with an apparent molecular weight of 34,000. The second gene (tetR) encompasses at least 650 base pairs and encodes a soluble 26,000-dalton protein, identified by complementation analysis as the repressor. The two adjacent genes have opposite transcriptional polarity, suggesting that the sites controlling their expression are located in the intercistronic region between tetA and tetR.

Plasmid ColVBtrp maintenance in Erwinia carotovora

Plasmid ColVBtrp maintenance in Erwinia carotovora cells was followed by measuring kinetics of elimination of plasmid genetic markers and loss of plasmid deoxyribonucleic acid. An E. carotovora mutant stably carrying plasmid ColVBtrp was isolated. Besides stable plasmid maintenance, the mutant showed altered sensitivity to male-specific phage MS2, sensitivity to drugs, and colony morphology.

Identification of the gene lon (capR) product as a 94-kilodalton polypeptide by cloning and deletion analysis

A mutation in the lon (capR) gene of Escherichia coli K-12 effects several phenotypic alterations in the mutant cell, such as overproduction of capsular polysaccharide and sensitivity to ultraviolet or ionizing radiation. A previously cloned 9.2-megadalton (Md) EcoRI fragment contained the capR+ gene and specified two polypeptides, 94 kilodaltons (K) and 67K. To provide evidence that the 94K polypeptide is the capR+ gene product, we constructed a capR+ plasmid pJMC40, having a 2.0-Md EcoRI-PstI fragment which codes only for the 94K polypeptide. Plasmids pJMC22 and pJMC30, having deletions of 0.7 and 0.8 Md, respectively, from one end of the 2.0-Md fragment, were also constructed. Each codes for a shortened stable polypeptide (from the 94K). Neither plasmid can confer the capR+ phenotype to capR mutants, confirming that the unaltered 94K polypeptide is the capR+ gene product. Plasmids pJMC51 and pJMC52 each have a deletion of 0.7 Md from the other end of the 2.0-Md fragment, differing only in the orientation of the remaining 1.3-Md fragment with respect to the cloning vehicle. They are nonfunctional with respect to capR+ and do not code for a common polypeptide from the 1.3-Md fragment. These data indicate that the fragments in pJMC22 and pJMC30, which both code for shortened 94K polypeptides, contain the promoter-operator region of the capR gene. The deletion plasmids were also used to map chromosomal capR mutations.

Copy number control and incompatibility of plasmid R1: identification of a protein that seems to be involved in both processes

Investigations into the genetic determinants for incompatibility of miniplasmids and hybrid replicons constructed from wide type and mutant R1 revealed the presence of an incompatibility function at the junction f two small PstI fragments. These two fragments were not distinguished in earlier experiments since they have the same mobility on agarose gels. This incompatibility function is distinct from other inc-determinants of R1 (Kollek and Goebel 1979; Molin and Nordström, 1980) and independent of R1-type replication. By means of specific deletions and subcloning of DNA fragments, the location of this new inc-determinant could be determined further. After deletion of this inc-determinant from inc-determinant from miniplasmids, a 5-fold increase in copy number was observed which could then be reduced to a copy number of about 1 plasmid per cell by complementation with hybrid plasmids having this function. Incompatibility of miniplasmids deleted in this determinant is not reduced, whereas analogous deletions introduced into recombinant plasmids nearly abolished their incompatibility. This determinant seems to exert strong incompatibility only when cloned on pBR322. Therefore, its main function is plasmid R1 is probably restricted to copy control. The appearance of low copy numbers of of miniplasmids carrying this determinant and of trans-acting copy control and strong incompatibility exerted by hybrid plasmids is consistently correlated with the presence of a protein of 11,000 molecular weight, synthesized in relatively large amounts in Escherichia coli minicells.

Competition between congenic Escherichia coli K-12 strains in vivo

The ability of Escherichia coli to colonize the large bowels of animals is related to many factors inherent to the intestinal environment and the bacterium. The use of germfree mice eliminates the competition between E. coli and the other microflora and allows most E. coli strains to colonize. We found that E. coli K-12 strains differing in chromosomal antibiotic resistance could monoassociate in germfree mice in large numbers. However, when two or more strains were in competition with each other, we detected quantitative differences in the abilities of the strains to colonize. The order of colonizing ability was as follows: nalidixic acid resistance greater than streptomycin resistance greater than rifampin resistance. We also found that a nalidixic acid-resistant strain bearing plasmid pBR322 colonized less efficiently and at lower levels when in competition with the nalidixic acid-resistant strain. Studies of the membrane proteins of the various strains indicated that changes in membrane proteins occurred concomitantly with altered resistance to antimicrobial agents. These results suggest that chromosomally linked alterations in antimicrobial sensitivity may also reflect changes in membrane proteins and a decreased ability to colonize mammalian intestines in otherwise isogenic bacterial strains.

Biochemical and immunological characterization of an R plasmid-encoded protein with properties resembling those of major cellular outer membrane proteins

MRB, a major R222 plasmid-encoded protein previously described by us, is synthesized in large amounts in host Escherichia coli cells, where it is located principally in the outer membrane. Most of this protein is also bound to the peptidoglycan layer in a form which is trypsin resistant. Its monomeric molecular weight is about 29,000, but it is isolated from cell membranes in aggregate molecular weights of more than 100,000. These properties demonstrate a strong similarity between MRB and porins, major outer membrane proteins of host E. coli cells. They suggest that MRB may have an as-yet unidentified transport function, as do cellular outer membrane proteins with similar biochemical properties. By using antiserum specific for MRB, we demonstrated identity between MRB and the product of the traT gene, one of the surface exclusion proteins on the F plasmid. The synthesis of MRB was found to be constitutive, in contrast to other tra genes, which appear to be under more rigid regulation by the tra operon. These findings suggest that on R222 and other F-like R plasmids this protein has its own promoter.

Plasmid cistrons controlling synthesis and excretion of the exotoxin alpha-haemolysin of Escherichia coli

The synthesis and secretion of the toxic exoprotein alpha-haemolysin of E. coli PM152 is coded by the transmissible plasmid pHly152 (41 x 10(6) dalton) as shown by the transformation of the plasmid DNA and the isolation of mutants that are specifically altered in the synthesis and transport of haemolysin. These mutants were obtained by chemical mutagenesis and insertion of the ampicillin transposon (Tn3) into pHly152. Tn3 transposition was also used for the identification and the location of the cistrons on pHly152 essential for haemolysis. The EcoRI and HindIII fragments of the haemolytic plasmid pHly152 were cloned and used for the complementation of the haemolysis negative Tn3 insertion mutants. A DNA segment of 3.2 x 10(6) dalton could be thus identified which consists of at least three clustered cistrons necessary for haemolysis. Two of these cistrons are required for the formation of active haemolysin. At least one other cistron seems to be involved in the secretion of active haemolysin through the outer membrane of E. coli. The gene products determined by these cistrons were identified in minicells of E. coli. Their molecular properties were determined and their possible function in the formation and secretion of haemolysin will be discussed.

Cloning the spoT gene of Escherichia coli: identification of the spoT gene product

We have isolated five specialized transducing lambda bacteriophages (lambda dpyrE spoT) carrying the pyrE and spoT genes of Escherichia coli. A fragment from one of these phages was used as the source of DNA to clone the spoT and pyrE genes on a multicopy plasmid, pBR322. Insertions and deletions in this plasmid were obtained. These plasmids were used to transform a minicell-producing strain, and the gene products synthesized were determined. Our experiments demonstrate that the spoT and pyrE genes are separated by about 4 magadaltons and suggest that the spoT gene product is a protein whose molecular weight is 80,000. The strain in which the spoT+ allele is carried on a plasmid produced nine times more spoT gene activity than a normal spoT+ strain when assayed in crude extracts. This strain was used to prepare partially purified gene product, guanosine 5'-diphosphate, 3'-diphosphate pyrophosphatase. The enzyme has the following characteristics. (i) It hydrolyzes pyrophosphate from the 5'-pyrophosphate of guanosine 5'-diphosphate, 3'-diphosphate, yielding GDP and pyrophosphate. (ii) Its activity is strongly stimulated by Mn2+ and slightly stimulated by salt. (iii) Its activity is inhibited by uncharged tRNA. There are also two additional activities in the cell extract which degrade guanosine in 5'-diphosphate, 3'-diphosphate in vitro but which are not specified by the spoT gene.

Propagation of restriction fragments from the mitochondrial DNA of Saccharomyces cerevisiae in E. coli by means of plasmid vectors

Some of the EcoRI fragments of yeast (Saccharomyces cerevisiae) mitochondrial DNA were cloned into E. coli using plasmid pMB9. The five smallest fragments in molecular weight appeared to be preferentially retained by E coli; partial fragments derived from larger mitochondrial DNA fragments were also found. One of the fragments, R7 (2.4 kb), may contain the OII gene. Cloned R7 DNA was stable under a variety of growth conditions, but showed some changes in molecular weight after transfer to different E. coli strains. Fragment R7 is transcribed in minicells, producing RNA that hybridizes specifically to mitochondrial DNA. Both DNA strands are transcribed, in contrast to the asymmetric transcription found in mitochondria. No new polypeptides were observed in minicells containing cloned fragment 7.

Cloned DNA fragment specifying major outer membrane protein a in Escherichia coli K-12

Plasmid pMC44 is a recombinant plasmid that contains a 2-megadalton EcoRI fragment of Escherichia coli K-12 DNA joined to the cloning vehicle, pSC101. The polypeptides specified by plasmid pMC44 were identified and compared with those specified by pSC101 to determine those that are unique to pMC44. Three polypeptides specified by plasmid pMC44 were localized in the cell envelope fraction of minicells: a Sarkosyl-insoluble outer membrane polypeptide (designated M2), specified by the cloned 2-megadalton DNA fragment, and two Sarkosyl-soluble membrane polypeptides specified by the cloning plasmid pSC101. Bacteria containing plasmid pMC44 synthesized quantities of M2 approximately equal to the most abundant E. coli K-12 outer membrane protein. Evidence is presented that outer membrane polypeptide M2, specified by the recombinant plasmid pMC44, is the normal E. coli outer membrane protein designated protein a by Lugtenberg and 3b by Schnaitman.

Isolation of a small DNA fragment carrying the gene for a dihydrofolate reductase from a trimethoprim resistance factor

DNA fragments of the R factor R388 which renders E. coli resistant to trimethoprim by inducing a trimethoprim resistant dihydrofolate reductase (Amyes and Smith, 1974) were inserted into plasmids and screened for the expression of the trimethoprim resistance gene. By means of a two step deletion procedure a 1770 bp EcoRI/BamH1 fragment was isolated which conferred drug resistance and which was found to induce the synthesis of the same dihydrofolate reductase as the parental R factor. Gene dosage experiments indicated that the induction was due to the presence of a dihydrofolate reductase structural gene on the 1770 bp fragment. The gene could be assigned to a segment which was less than 1200 bp long. The 1770 bp fragment and a recombinant plasmid consisting of pSF2124 and part of R388 were mapped with several restriction nucleases. The R factor induced enzyme was partially purified from a strain carrying a multicopy recombinant plasmid into which the 1770 bp fragment was inserted and which induced high levels of dihydrofolate reductase. The enzyme was found to be stable at 100 degrees. Some aspects of the synthesis of dihydrofolate reductase are discussed.

Application of R-plasmid DNA's from Escherichia coli minicells in genetic transformation

Components of minicell lyzates of Escherichia coli P678.54 (R1 drd 19) and escherichia coli P678.54 (R6K) were visualized in an electron microscope and used for the transformation of Escherichia coli JC7623. The frequency of the resulting transformants (of the order of 10(-6)%) was not appreciably influenced by the manner of lyzate preparation. The presence of covalently closed circular DNA was detected in two different transformants using radioisotopes, thus demonstrating an autonomous existence of R1 drd 19 or R6K plasmids in tested transformants. This finding corresponds with the results of their genetic analysis.

Isolation and characterization of the minimal fragment required for autonomous replication ("basic replicon") of a copy mutant (pKN102) of the antibiotic resistance factor R1

The mini plasmids deriving from pKN102, a copy mutant of the antibiotic resistance factor R1drd-19 of E. coli, share a common DNA sequence of 2.6 kb, which carries the minimal functions for autonomous replication. By cloning of two PstI fragments of this region it could be demonstrated that the "basic replicon" is a DNA segment not larger than 1.8 kb, which carries the orgin of replication and the genetic information for at least two proteins. Protein F (NW=11.000 dalton) seems to be synthesed in larger amounts in minicells of E. coli than protein C (20.000). Plasmids containing this isolated replicon of R1 are completely compatible with the parental plasmid R1drd-19.

Mucopeptide biosynthesis by minicells of Escherichia coli

Minicells produced by Escherichia coli chi925 incorporated amino acids and N-acetyl-d-glucosamine into mucopeptide.

Synthesis of cell envelope components by anucleate cells (minicells) of Bacillus subtilis

Minicells produced by Bacillus subtilis CU403 (divIVB1) are capable of mucopeptide biosynthesis as shown by the incorporation of L-alanine, D-alanine, and N-acetylglucosamine into trichloroacetic acid-precipitable material, which can be degraded to trichloroacetic acid-soluble material by lysozyme digestion. Incorporation of the precursors is sensitive to vancomycin and D-cycloserine and insensitive to chloramphenicol. Penicillin inhibits the incorporation of D- and L-alanine N-acetylglucosamine at concentrations in excess of 10 mug of penicillin per ml; however, minicells are insensitive to penicillin-induced lysis. The material synthesized in minicells from N-acetylglucosamine is not subject to turnover during a subsequent 6-h incubation period. [2-3H]glycerol is converted to a cold trichloroacetic acid-precipitable form by minicells. This synthesis is not inhibited by vancomycin, penicillin, D-cycloserine, or chloramphenicol. Fractionation of the material synthesized from glycerol into hot trichloroacetic acid-soluble material and chloroform/methanol-extractable material indicates that minicells convert glycerol into teichoic acid and lipid.

Protein expression in E. coli minicells by recombinant plasmids

The polypeptides synthesized in E. coli minicells from recombinant plasmids containing DNA fragments from cauliflower mosaic virus, Drosophila melanogaster, and mouse mitochondria were examined. Molecularly cloned fragments of cauliflower mosaic virus DNA directed the synthesis of high levels of three polypeptides, which were synthesized entirely from within the cloned virus DNA fragments independent of their insertion into the plasmid vehicles. Several fragments of D. melanogaster DNA were capable of initiating polypeptide synthesis; however, termination of these polypeptides was dependent upon the insertion into the plasmid vehicle. The majority of D. melanogaster DNA fragments examined did not direct the detectable synthesis of any polypeptides. Insertion of DNA into the Eco RI site of ColE1 and pSC101 plasmids resulted in the altered expression of plasmid-encoded polypeptides. In the case of ColE1, this site of insertion lies within the colicin E1 structural gene, and insertion of foreign DNA into the site results in the synthesis of an inactive truncated colicin E1 molecule. It is probable that the Eco RI site in pSC101 lies within the structural gene for a polypeptide involved in tetracycline resistance, and insertion of DNA into this site may also result in the synthesis of a truncated or elongated polypeptide.

New mini-ColE1 as a molecular cloning vehicle

A new mini-ColE1 plasmid, designated pAC105, was isolated. It has a molecular weight of 1.6 X 10(6) and carries information for its self-replication as well as information for conferring colicin E1 immunity upon its host. Furthermore, pAC105 undergoes replication in the presence of chloramphenicol even when a foreign deoxyribonucleic acid (pSC101) is inserted into its single EcoRI restriction site. Studies in minicell-producing strains demonstrate that pAC105 codes for only two or three polypeptides of low molecular weight. The advantages of using it as a molecular cloning vehicle are discussed.

Synthesis of an R plasmid protein associated with tetracycline resistance is negatively regulated

Synthesis of proteins encoded by the R222 plasmid was observed in a DNA-directed cell-free system and the products were compared to those plasmid proteins synthesized in Escherichia coli minicells. A greater number of plasmid-specified proteins was detected in the in vitro system than in the minicell, suggesting the presence of control factors for plasmid gene expression in the minicell. Synthesis of a newly detected plasmid protein (TET protein) is induced by tetracycline in minicells containing tetracycline-resistant plasmids, including R222, and this induced synthesis correlates with induced host resistance to the drug. This TET protein was synthesized in vitro from R222 DNA in the absence of tetracycline, indicating that no positive regulatory role for tetracycline is required for the protein's synthesis. TET proteon synthesis was inhibited in vitro when cell-free extracts prepared from cells containing the R222 plasmid were used.

Very stable prokaryotic messenger RNA in chromosomeless Escherichia coli minicells

E. coli minicells lack DNA, yet they make protein, the synthesis of which is sensitive to chloramphenicol but insensitive to rifamycin. This protein is coded for by very stable cellular mRNA with an estimated half-life of 40-80 min. In an R factor-containing minicell, two very different species of mRNA are observed: (i) R factor-specific mRNA with a short half-life whose synthesis is rifamycin-sensitive and (ii) cellular mRNA with a long half-life whose synthesis is rifamycin-insensitive. These findings indicate that minicells contain normal degradative mechanisms for mRNA and point out the existence of a unique class of very stable cellular mRNA. Greater than 80% of the rifamycin-insensitive protein synthesized goes into the outer minicell membrane. Relatively stable mRNA, half-life 5.5-11.5 min, for outer membrane protein in whole cells has been reported [Hirashima et al. (1973) J. Mol. Biol. 79, 373-389]. The stability of minicell mRNA is significantly greater. This and other observations suggest that there are two functional species of mRNA for outer membrane protein perhaps in different sites in the cell. Furthermore, these studies suggest that a class of cellular proteins is synthesized in bacteria without concomitant transcription and in the absence of association with chromosomal DNA.

Segregation into the replication of bacteriophage M 13 DNA in minicells of Escherichia coli

Minicells derived from E. coli x796(F+) are refractory to infection by phage M 13. However, after infection of the minicell-producing strain with M 13, phage DNA is found to segregate efficiently into newly formed minicells. The M 13 specific DNA present in minicells isolated several hours after infection consists of single stranded viral DNA and double stranded replicative forms in nearly equal amounts. M 13 DNA containing minicells are capable of carrying out at least one complete round of single stranded DNA synthesis as shown by the flow of label from replicative forms to free single strands.

DNA degradation in minicells of Escherichia coli K-12. II. Effect of recA1 and recB21 mutations on DNA degradation in minicells and detection of exonuclease V activity

The properties of minicell producing mutants of Escherichia coli deficient in gentic recombination were examined. Experiments were designed to test recombinant formation in conjugal crosses, survival following UV-irradiation in cells, and the state of DNA metabolism in minicells. The REC- phenotypes are unaffected by min+/- genotypes in whole cells. In contrast to minicells produced by rec+ parental cells, minicells from a recB21 strain have limited capacity to degrade linear, Hfr transfereed DNA. The lack of a functional recA gene product, presumably involved in inhibiting the recBC nuclease action(s), permits unrestricted Hfr DNA breakdown in minicells produced by a recA1 strain. This results in an increase in TCA soluble products and in the formation of small DNA molecules that sediment near the top of an alkaline sucrose gradient. Unlike the linear DNA, circular duplex DNA from plasmids R 64-11 or lambdadv, segregated into the minicells, is resistant to breakdown. By using in vitro criteria, and [32P]-labelled linear DNA from bacteriophage T7 for substrate, we found that the ATP-dependent exonuclease of the recBC complex (exo V) is present in rec+ and recA- minicells, and is lacking in the recB21 mutant. In fact, the absence of a functional exo V in recBC- minicells results in isolation of larger than average Hfr DNA from minicells. We suggest that recombination (REC) enzymes segregate into the polar minicells at the time of minicell biogenesis. This system should be useful for studies on DNA metabolism and functions of the recBC and recA gene products.

R factor proteins synthesized in Escherichia coli minicells: membrane-associated R factor proteins

R factor proteins are synthesized in R factor-containing Escherichia coli minicells. Half of this protein remained associated with the minicell membrane upon lysis of the minicells. Over 90% of the membrane-associated protein was extracted by sodium lauryl sarcosinate, suggesting a location of these proteins in the inner membrane. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of these membrane preparations demonstrated the presence of multiple peptides, including a prominent band with a molecular weight of 28,000 to 30,000. A polypeptide of similar size was seen in membrane preparations from minicells harboring R factors from five different compatibility types. This major R factor membrane peptide was seen with R factors repressed or derepressed for pilus synthesis, with and without antibiotic resistances. It was associated with R factor deoxyribonucleic acid in membrane-deoxyribonucleic acid complexes. Its possible role in R factor replication and/or transfer is being investigated.