The generation of a ColE1-Apr cloning vehicle which allows detection of inserted DNA

Cointegrate formation between homologous plasmids in Escherichia coli

Conjugation experiments were performed in which the donor was Escherichia coli K-12 strain KP245 containing either R plasmid NR1 plus an ampicillin-resistant derivative of ColE1 (*ColE1::Tn3, called RSF2124) or NR1 plus RSF2124 carrying a cloned EcoRI fragment of NR1. The recipient was the polA amber mutant JG112, in which RSF2124 cannot replicate. Ampicillin-resistant transconjugants can arise only when the genes for ampicillin resistance are linked to NR1 or are transposed to the host chromosome. When EcoRI fragment A of NR1 (20.5 kilobases) was cloned to RSF2124, the frequency of cotransfer of ampicillin resistance with tetracycline resistance was 25 to 60%. Plasmid DNA from these ampicillin-resistant transconjugant cells was analyzed by gel electrophoresis and was shown to be a cointegrate of NR1 and the RSF2124 derivative. Analysis of plasmid DNA isolated from donor cultures showed that the cointegrates were present before conjugation, which indicates that the mating does not stimulate cointegrate formation. When the cloned fragment was EcoRI fragment H of NR1 (4.8 kilobases), the frequency of cotransfer of ampicillin resistance with tetracycline resistance was about 4%, and the majority of the ampicillin-resistant transconjugants were found to contain cointegrate plasmids. When the donor contained NR1 and RSF2124, the frequency of cotransfer of ampicillin resistance was less than 0.1%, and analysis of plasmid DNA from the ampicillin-resistant transconjugants showed that Tn3 had been transposed onto NR1. These data suggest that plasmids which share homology may exist in cointegrate form to a high degree within a host cell.

Construction and physical mapping of plasmids containing the metJBLF gene cluster of E. coli K12

In vitro recombination techniques were used to clone the E. coli metJBLF gene cluster in a plasmid vector. Several chimeric plasmids were obtained, analyzed by restriction mapping and characterized genetically. The combined results establish that the met gene cluster is contained on an approximately 5.6 kilobase segment of bacterial DNA with metL between metB and metF. The origin of metL was localized precisely by its DNA sequence and its transcription direction was established.

Penicillinase-producing Neisseria gonorrhoeae: a molecular comparison of 5.3-kb and 7.4-kb beta-lactamase plasmids

Restriction endonuclease analysis and heteroduplex studies indicate that the only difference between the 5.3-kilobase (kb) and 7.4-kb plasmids from beta-lactamase-producing Neisseria gonorrhoeae is that the latter is the 5.3-kb plasmid with a 2.1-kb insertion. The insertion is bounded by inverted repeats of approximately 300 base pairs. Several plasmids from beta-lactamase-producing N. gonorrhoeae isolated at different times and in different countries were compared. Nine 5.3-kb plasmids were examined and found to be indistinguishable, as were sixteen 7.4-kb plasmids.

Biochemical characterization of HgCl2-inducible polypeptides encoded by the mer operon of plasmid R100

Minicells carrying the subcloned mer operon from plasmid R100 were pulse-labeled with [35S]methionine, and the labeled polypeptides were analyzed at various subsequent times by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The Hg(II) reductase monomer encoded by plasmid R100 occurred as two proteins of 69 and 66 kilodaltons (kd). The minor 66-kd protein is a modified form of the 69-kd protein. This modification occurs in vivo. Both of these mer proteins are found in the soluble fraction of the cell; however, the 66-kd protein appears to have a slight affinity for the cellular envelope. Both the 69- and 66-kd mer proteins have pI values greater (pI = 5.8) than that reported (pI = 5.3) for the analogous monomer encoded by plasmid R831. The 15.1- and 14-kd mer proteins are localized in the inner membrane and are probably elements of the mer-determined Hg(II) uptake system. These two mer membrane proteins, which are antigenically unrelated to the Hg(II) reductase monomer, are quite basic (pI values greater than 7.8). The 12-kd mer protein is also a basic polypeptide that is present in the soluble fraction of the cell. Unlike the two membrane-bound mer proteins, the 12-kd mer protein is processed from a 13-kd precursor.

Direct participation of lexA protein in repression of colicin E1 synthesis

Spontaneous colicin E1 production by plasmid RSF2124 in a recA lexA(spr) strain of Escherichia coli was about 10-fold greater than that observed in a wild-type strain. The synthesis was repressed nearly to the level of a recA strain in the presence of the plasmid pMCR551, which carries the lexA gene.

Influence of phage T3 and T7 gene functions on a type III(EcoP1) DNA restriction-modification system in vivo

The ocr+ gene function (gp 0.3) of bacteriophages T3 and T7 not only counteracts type I (EcoB, EcoK) but also type III restriction endonucleases (EcoP1). Despite the presence of recognition sites, phage DNA as well as simultaneously introduced plasmid DNA are protected by ocr+ expression against both the endonucleolytic and the methylating activities of the EcoP1 enzyme. Nevertheless, the EcoP1 protein causes the exclusion of T3 and T7 in P1-lysogenic cells, apparently by exerting a repressor-like effect on phage gene expression. T3 which induces an S-adenosylmethionine hydrolase is less susceptible to the repressor effect of the SAM-stimulated EcoP1 enzyme. The abundance of EcoP1 recognition sites in the T7 genome is explained by their near identity with the T7 DNA primase recognition site.

Conjugative R plasmids in Streptococcus faecium (group D)

Ten isolates of Streptococcus faecium were found to be resistant to penicillin, tetracycline, macrolides and related drugs, streptomycin, and kanamycin, and four strains were resistant to chloramphenicol. Six of these 10 strains transferred all their resistance markers (except penicillin) by conjugation at a low frequency (10(-7) to 10(-9)). Several plasmids of different molecular weights were found in each of the wild-type strains. In 5 of 11 transconjugant strains, R plasmids were detected which had molecular weights identical to those of the plasmids found in the corresponding donor strain. Each of the six other transconjugants harbored one plasmid with a size different from those found in the corresponding donor strain, suggesting the occurrence of molecular events during or after conjugative transfer. None of the five tetracycline-resistant transconjugants contained detectable satellite DNA, HindIII restriction enzyme fingerprints of S. faecium resistance plasmids were different from the HindIII patterns of macrolide, aminoglycoside, and tetracycline resistance plasmids from other strains of streptococci.

Read-through transcription from a derepressed Tn3 promoter affects ColE1 functions on a ColE1::Tn3 composite plasmid

Mutations in the repressor encoded by the transposon Tn3 tnpR gene lead to increased levels of expression of two gene products: the mutant repressor (TnpR-) and the Tn3 encoded transposase, TnpA (Heffron et al. 1978; Chou et al. 1979a). Derivatives of the ColE1::Tn3 composite plasmid, RSF2124, with mutant Tn3 repressor exhibited the expected elevated levels of transposition. Unexpectedly, hosts containing these tnpR- derivatives produced enhanced levels of the ColE1 encoded toxin, colicin E1. The gene for colicin E1 maps far (0.23-0.98 MU) from the Tn3 insertion point (0.73 MU) (Fig. 1). The colicin E1 overproduction phenotype, designated Eop-, was complemented in trans by wild type repressor gene product (TnpR+) to the wild type phenotype, Eop+. Hosts with RSF2124 derivatives which expressed high levels of both mutant repressor and mutant transposase (TnpR-, TnpA-) were Eop-. Hosts containing plasmids deleted for both tnpA and tnpR promoters were Eop+, while hosts with plasmids carrying a lac promoter substitution for the tnpA promoter were Eop-. These data support the idea that a cis-acting effect of increased transcription from the tnpA promoter into adjacent ColE1 DNA was the cause of colicin overproduction. Increased transcription activated a putative colicin augmentation function (caf) whose presence was required for the Eop- phenotype. Deletion mapping established that one boundary of the caf locus lies within 52 bases of the junction of the left end of Tn3 and ColE1 DNA. ColE1 DNA in this area contains an open reading frame which could encode either a 74 or a 63 residue protein (B. Polisky, unpublished DNA sequence data). The presence of increased levels of an mRNA transcript from this region and/or the increased expression of protein(s) from this transcript could result in an Eop- phenotype. Expression of the Eop- phenotype requires the presence of the host recE gene. Evidence is presented which suggests that the recA repressor, lexA protein, controls expression of the recE gene product, ExoVIII.

Characterization of ampicillin resistance plasmids from Haemophilus ducreyi

Seven strains of Haemophilus ducreyi from diverse geographic origins were analyzed for their plasmid content. All strains were multiply resistant, but only resistance to ampicillin was transferred to Escherichia coli by transformation. The H. ducreyi plasmids encoding for ampicillin resistance were 7.4, 5.7, and 3.6 megadaltons and encoded for part or all of TnA, and ampicillin transposon. The relatedness of these plasmids was examined by restriction endonuclease digestion and DNA-DNA homology with isolated DNA fragments from TnA.

The nucleotide sequence of the bacteriocin promoters of plasmids Clo DF13 and Co1 E1: role of lexA repressor and cAMP in the regulation of promoter activity

Treatment of cells, harbouring the bacteriocinogenic plasmic Clo DF13 with mitomycin-C, which induces the cellular SOS response, results in a significantly increased transcription of the operon encoding the bacteriocin cloacin DF13, the immunity protein and the lysis protein H. The nucleotide sequences of the promoter regions and N-terminal parts of the bacteriocin genes of Clo DF13, Col E1 and the pMB1 derivative pBR324 have been determined. A comparison of these sequences with those of corresponding regions of the lexA, recA and uvrB genes revealed that the promoter regions of the bacteriocin genes studied contain binding sites for the lexA protein, which is the repressor of the E. coli DNA-repair system. Using both, a thermosensitive lexA host strain and a host with pACYC184 into which the lexA gene had been cloned, we were able to demonstrate, that in vivo the lexA protein is involved in the regulation of bacteriocin synthesis. From the data presented, we conclude that bacteriocin synthesis is controlled at least by the lexA repressor. It has been reported that also catabolite repression might play an essential role in the control of bacteriocin synthesis. Computer analysis of the DNA sequence data indicated that the promoter regions of both, the cloacin DF13 and colicin E1 genes contain potential binding sites for the cyclic AMP-cyclic AMP Receptor Protein complex.

Heterogeneity of tetracycline resistance determinants in Streptococcus

We found that naturally occurring tetracycline resistance in streptococci is encoded by more than one genetic determinant. Two of these distinct determinants were cloned, and the regions that are necessary and sufficient for expression of tetracycline resistance were defined by deletion analysis. These cloned determinants were further characterized by DNA-DNA hybridization experiments which also identified a third genetically unrelated tetracycline resistance determinant. Some of these genetic differences appear to represent mechanistic differences. The tetL determinant was associated with small nonconjugative plasmids and mediated resistance to tetracycline. The tetM determinant was most often "nonplasmid" associated and mediated resistance to minocycline as well as tetracycline. The tetN determinant was represented on a large conjugative plasmid and was genetically distinct from tetL and tetM, although phenotypically it resembled tetM.

Cloning vectors derived from bacterial plasmids

A wide variety of plasmid cloning vectors, most of which utilize the basic Co1E1I replicon have been constructed. Utilizing these vectors, in conjunction with the newly developed techniques of gene isolation and oligonucleotide synthesis, essentially any gene which can be identified can be cloned. We anticipate that future work in this area will be directed at improving techniques for the regulated expression of cloned genes and the further development of plasmid replicons in which the copy number can be readily controlled.

Molecular cloning of the tolC locus of Escherichia coli K-12 with the use of transposon Tn10

We have cloned the tolC gene of E. coli K-12 into pSF2124 by using transposon Tn10 as the marker to first isolate the relevant DNA fragment. The gene is on a 10.5 kb EcoRI fragment, and Tn5 insertion mutagenesis locates the gene near one end of this EcoRI fragment. An EcoRI-PstI fragment has been subcloned into pBR322 to facilitate further analysis of the gene.

Purified glucocorticoid receptors bind selectively in vitro to a cloned DNA fragment whose transcription is regulated by glucocorticoids in vivo

Activated glucocorticoid receptor protein, purified to 40-60% homogeneity from rat liver extracts, binds selectively in vitro to a cloned fragment of murine mammary tumor virus (MTV) DNA. The DNA fragment tested contains about half of the sequences present in intact MTV DNA, and its rate of transcription, like that of the intact viral element, is strongly stimulated by glucocorticoids when it is introduced into the genome of a receptor-containing cell. In contrast, the receptor fails to bind selectively to DNA restriction fragments from E. coli plasmids pBR322 and RSF2124 or from bacteriophages lambda and T4. Preliminary experiments to localize regions within MTV DNA responsible for selective binding have revealed thus far one subfragment that fails to bind the receptor and one selectively bound subfragment that maps far downstream from the 5' terminus of the normal RNA transcript. These studies are consistent with the notion that steroid receptors may modulate rates of transcription by recognizing specific DNA sequences within or near the regulated genes.

Complementation of replication-deficient deletion derivatives of plasmid mini-F

Deleted mini-F plasmids with defects in replication were constructed and tested to see whether they could be rescued through complementation by a helper plasmid. This allowed us to identify two genetic loci determining trans-acting functions required for stable maintenance of plasmid mini-F, one encoded by the PstI fragment from 45.7 to 47.3 F-coordinates (F) and the other most probably located in the region from 43.1 to 43.8 F. The smallest mini-F plasmid that could be established through complementation consists of the PstI fragment 44.0 to 45.7 F, encoding origin II and the incB locus.

Molecular cloning and expression of the ilvGEDAY genes from Salmonella typhimurium

The ilvGEDAY genes of Salmonella typhimurium were cloned in Escherichia coli K-12 by in vitro recombination techniques. A single species of recombinant plasmid, designated pDU1, was obtained by selecting for Valr Ampr transformants of strain SK1592. pDU1 was shown to contain a 14-kilobase EcoRI partial digestion product of the S. typhimurium chromosome inserted into the EcoRI site of the pVH2124 cloning vector. The ilvGEDAY genes were found to occupy a maximum length of 7.5 kilobases. Restriction endonuclease analysis of the S. typhimurium ilv gene cluster provided another demonstration of the gene order as well as established the location of ilv Y between ilvA and ilvC. The presence of a ribosomal ribonucleic acid operon on the pDU1 insert, about 3 kilobases from the 5' end of ilvG, was shown by Southern hybridization. The expression of the ilvGEDA operon from pDU1 was found to be elevated, reflecting the increased gene dosage of the multicopy plasmid. A polarity was observed with respect to ilvEDA expression which is discussed in terms of the possible translational effects of the two internal promoter sequences, one located proximal to ilvE and the other located proximal to ilvD.

Translocation of sequences encoding antibiotic resistance from the chromosome to a receptor plasmid in Salmonella ordonez

Salmonella ordonez strain BM2000 carries kanamycin (Km), ampicillin (Ap), spectinomycin (Sp), chloramphenicol (Cm), tetracycline (Tc), and sulfonamide (Su) resistance and production of colicin Ib (Cib). The Km and Cib characters were carried by a 97 kb IncI1 plasmid (pIP565). In addition to the Km and Cib traits, all or part of the other antibiotic resistance (R) determinants could be transferred by conjugation from S. ordonez to Escherichia coli where all the acquired characters are borne by an IncI1 plasmid, designated complete or partial composite plasmid respectively. DNA from pIP565 and composite plasmids and total DNA from strain BM2000 were studied by agarose and polyacrylamide gel electrophoresis following digestion with restriction endonucleases, and by Southern hybridization. These comparative analyses enabled us a) to show that acquisition by pIP565 of resistance to all or some of the antibiotics was due to the insertion of a single DNA fragment into the receptor plasmid; b) to detect two types of composite plasmids with regard to the specificity of insertion into pIP565 and the mapping of the inserts; c) to demonstrate that the ApCmSpSuTc resistance determinants were integrated into S. ordonez BM2000 chromosomal DNA; d) to map the restriction fragments of the translocatable sequence integrated into strain BM2000 chromosome or into pIP565. The results obtained suggest that two distinct mechanisms for the translocation of the R determinants coexist in S. ordonez BM2000. Recombination between two of the four directly repeated copies of the IS-like sequence (IS1522) present in S. ordonez chromosome leads to the circularisation of all or part of the ApCmSpSuTc R determinants and is followed by either 1) a second recombination with the copy of IS1522 in pIP565 (Type I composite plasmids), or 2) transposition of precise groups of characters in various sites of pIP565 (Type II composite plasmids).

Purification and properties of the restriction endonuclease BglII from Bacillus globigii

The restriction endonuclease BglII from Bacillus globigii has been purified to homogeneity. The enzyme is a dimer of two subunits of Mr = 27000. The reaction mechanism does not involve the accumulation of a DNA intermediate nicked in one strand and the enzyme is not affected by superhelical twists in the substrate DNA, indicating that DNA binding does not involve either winding or unwinding of the double helix. Antibodies were prepared against BglII. These antibodies did not cross react with any other restriction endonucleases tested, including other enzymes from B. globigii or from closely related strains. It is thus unlikely that type II restriction enzymes represent a closely related group of proteins.

Characterization of the respiratory NADH dehydrogenase of Escherichia coli and reconstitution of NADH oxidase in ndh mutant membrane vesicles

Highly purified preparations of the cholate-solubilized respiratory NADH dehydrogenase, isolated from genetically amplified Escherichia coli strains [Jaworowski, A., Campbell, H. D., Poulis, M. I., & Young, I. G. (1981) Biochemistry 20, 2041-2047], have been characterized. Enzyme preparations were shown to contain 70% (w/w) lipid, predominantly phosphatidylethanolamine. One mol of noncovalently bound FAD and approximately 1 mol of ubiquinone/mol of enzyme subunit were detected. The purified enzyme was shown to contain only low levels of Fe and acid-labile S, indicating the absence of iron-sulfur clusters. No Cu, Mo, W, or covalently bound P was detected, and no evidence for other chromophores was obtained from visible and ultraviolet absorption spectra of the purified enzyme or of the delipidated polypeptide prepared by gel filtration in sodium dodecyl sulfate. Protein chemical studies verified that the enzyme consists of a single polypeptide species of Mr 47 000, and the N- and C-terminal cyanogen bromide peptides were identified. The pure enzyme was shown to reconstitute membrane-bound, cyanide-sensitive NADH oxidase activity in membrane vesicles prepared from ndh mutant strains.

The chloroplast genome of bleached mutants of Euglena gracilis

Bleached mutants of Euglena gracilis, traditionally thought to be completely deprived of chloroplast DNA, have been shown to contain a defective chloroplast genome, present at a very low copy number, and preferentially retaining ribosomal RNA genes. We propose to call these mutants phi-, because of their resemblance with the rho- mutants of yeast.

Analysis of a dispersed repetitive DNA sequence in isogenic lines of Drosophila

The location of sequences homologous to a cloned D. melanogaster DNA segment, Dm 25, has been examined in polytene chromosomes by hybridization in situ. Dm 25 localizes to multiple sites and shows variation in patterns between different strains and among individuals within wild-type laboratory strains. Analysis of numerous geographically distinct isogenic lines suggests that Dm 25 patterns are determined by germ-line factors and are not the product of strictly somatic events. In general there is wide variation in Dm 25 patterns among different lines, but a significant number of sites are common to two or more distinct lines. Hybridization to restriction digests of genomic DNA suggests that Dm 25 is a moderately repetitive, conserved sequence whose copies are dispersed throughout the genome. Analysis of species other than melanogaster indicates a significant divergence in structure of sequences homologous to Dm 25 as well as a drastic reduction in amount of homology to the melanogaster sequence.

Genetic identification and purification of the respiratory NADH dehydrogenase of Escherichia coli

Escherichia coli membrane particles were solubilized with potassium cholate. An NADH:ubiquinone oxidoreductase was resolved by hydroxylapatite chromatography of the solubilized material. This enzyme has been identified as the respiratory NADH dehydrogenase since it is absent in chromatograms of solubilized material from an ndh mutant strain. Such mutants lack membrane-bound NADH oxidase activity and have previously been shown to have an inactive NADH dehydrogenase complex [Young, I. G., & Wallace, B. J. (1976) Biochim. Biophys. Acta 449, 376-385]. The respiratory NADH dehydrogenase was amplified 50- to 100-fold in vivo by using multicopy plasmid vectors carrying the ndh gene and then purified to homogeneity on hydroxylapatite. Hydroxylapatite chromatography of cholate-solubilized material from genetically amplified strains purified the enzyme approximately 800- to 100-fold relatively to the activity in wild-type membranes. By use of a large-scale purification procedure, 50-100 mg of protein with a specific activity of 500-600 mumol of reduced nicotinamide adenine dinucleotide oxidized min-1 mg-1 at pH 7.5, 30 degrees C, was obtained. Sodium dodecyl sulfate gel electrophoresis of the purified enzyme showed that the enzyme consists of a single polypeptide with an apparent Mr of 45 000.

Tetracycline resistance genes from Bacillus plasmid pAB124 confer decreased accumulation of the antibiotic in Bacillus subtilis but not in Escherichia coli

Expression of tetracycline resistance by genes originating in the Bacillus plasmid pAB124 was examined in both Bacillus subtilis and Escherichia coli host cells. Expression of resistance in B. subtilis by genes from pAB124 was inducible and associated with decreased accumulation of the antibiotic. A fragment of pAB124 carrying the genes coding for tetracycline resistance was cloned into the E. coli plasmid RSF2124. The cloned fragment conferred a low level of resistance in E. coli, but this was not associated with decreased uptake of tetracycline and was not inducible.

Identification and cloning of the genetic determinant that encodes for the K88ac adherence antigen

Strains of Escherichia coli capable of causing diarrhea in young pigs are often able to proliferate in the upper small intestine of the infected animal due to the presence of a specific surface antigen, K88. The genetic determinants for K88 antigen production and the ability to utilize the trisaccharide raffinose (Raf) are carried on a 50-megadalton plasmid. Recombinant deoxyribonucleic acid techniques were used to insert an 8.2-megadalton HindIII fragment carrying the K88ac gene(s) from the K88/Raf plasmid pPS100 into the vector pBR322. At lease six polypeptides encoded by this fragment were expressed in minicells. These polypeptides ranged in size from 18,000 to 70,000 daltons. The K88ac antigenic subunit, which has an apparent molecular weight of 23,500, was identified by immunoprecipitation with staphylococcal protein A as the coprecipitant.

Determination of the functions of hemolytic plasmid pHly152 of Escherichia coli

The alpha-hemolytic Escherichia coli strain PM152 harbors three transmissible plasmids, which have molecular weights of 65 X 10(6) (pA152), 41 X 10(6) pHly152), and 32 X 10(6) (pC152). Plasmids pHly152 and pC152 belong to incompatibility groups J2 and N, respectively. By transforming E. coli K-12 with isolated plasmids, we showed that the genetic determinant required for hemolysis was located entirely on plasmid pHly152, and a physical map of this plasmid was constructed. By transposon mutagenesis, a deoxyribonucleic acid segment of about 3.5 X 10(6) daltons was identified as being essential for hemolysis. Most of the EcoRI and HindIII fragments of the hemolytic plasmid pHly152 were cloned by using pACYC184 and RSF2124 as vectors. Two classes of Tn3-induced hemolysis-negative mutants could be complemented by recombinant plasmids carrying fragments from the hemolysis region of pHly152, whereas a third class could be restored to hemolytic activity only by recombination between the mutant plasmids and a suitable recombinant deoxyribonucleic acid. These data suggest that there are at least three clustered cistrons which are required for hemolysis. Other EcoRI and HindIII fragments of pHly152 were identified as being essential for replication, incompatibility, transfer, and restriction.

Regulation of plasmid DNA synthesis: isolation and characterization of copy number mutants of miniR6-5 and miniF plasmids

Copy number (Cop) mutants of miniR6-5 and miniF plasmid derivatives containing a beta-lactamase gene were isolated by selection for increased ampicillin-resistance. Mutants which exhibited an increased copy number and a reduced incompatibility response as compared to the respective parent mini-plasmid were obtained from both miniR6-5 and miniF. Characterization of these mutant plasmids has provided the first description of the replicative properties of miniF Cop mutants, and has also facilitated a comparison of plasmids representing the IncFI and IncFII incompatibility groups. Cop mutants from these groups differed in several respects: (i) MiniF Cop mutants were considerably more difficult to obtain and showed a markedly lower transforming efficiency than the corresponding miniR6-5 mutants. (ii) MiniR6-5 Cop mutants were stably maintained in a polA1 strain without selective pressure, whereas miniF Cop mutants severely reduced the viability of this host. (iii) MiniR6-5 replication stopped within a few minutes after inhibition of protein synthesis, whereas miniF replication continued at a declining rate for about one hour in the presence of chloramphenicol. (iv) In contrast to miniR6-5 replication, miniF DNA synthesis was blocked faster by rifampicin than by chloramphenicol. (v) The copy number of miniR6-5 plasmids (but not of miniF) was reduced by about 50% in an rnc strain deficient in RNAase III.

An unusual RNA polymerase binding site in the immunity region of phage lambda

RNA polymerase binds very tightly at a site called Brex in the lambda immunity region, to the left of the rex gene and about 600 nucleotides to the right of PL. The complex formed is resistant to 1 M NaCl in the absence of nucleotide triphosphate. While in vitro little or no transcription is observed from Brex, in vivo, when inserted in a plasmid vector which allows detection of its activity, it acts as an efficient promoter. We have mapped the site protected by RNA polymerase against DNase and determined its sequence which is abnormal compared that of an average promoter.

Sequence-specific recombination of plasmid ColE1

The conjugal transmission of plasmid ColE1 and its derivatives can lead to recA-independent recombination. The recombination is not observed during vegetative growth and takes place specifically between the sequences that are thought to represent the transfer origin of ColE1. This provides genetic evidence for breakage and reunion events during the transmission of ColE1.

Coordinate expression of Escherichia coli dnaA and dnaN genes

The defects of temperature-sensitive dnaA and dnaN mutants of Escherichia coli are complemented by a recombinant lambda phage, which carries the bacterial DNA segment composed of two EcoRI segments of 1.0 and 3.3 kilobases. Derivatives of the phage, which have an insertion segment of Tn3 in the dnaA gene, are much less active in expressing the dnaN gene function than the parent phage. The dnaN gene activity was determined as the efficiency of superinfecting phage to suppress loss of the viability of lambda lysogenic dnaN59 cells at the non-permissive temperature. Deletions that include the end of the dnaA gene distal to the dnaN gene also reduce the expression of the dnaN gene function. Deletion and insertion in the dnaN gene do not affect the expression of the dnaA gene function. The expression of the dnaN gene function by the dnaA- dnaN+ phages remains weak upon simultaneous infection with dnaA+ dnaN- phages. Thus the insertion and deletion of the dnaA gene influence in cis the expresion of the dnaN gene. We propose that the dnaA and dnaN genes constitute an operon, where the former is upstream to the latter.

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.

Sequence of the distal tRNA1Asp gene and the transcription termination signal in the Escherichia coli ribosomal RNA operon rrnF(or G)

Several DNA fragments carrying tRNA genes have been cloned from EcoRI endonuclease digests of Escherichia coli DNA. Using cloned DNA, the sequence of the region around the distal gene for tRNA1Asp (F(or G)) in the E. coli ribosomal RNA operon [rrnF(or G)] has been determined. In the distal portion of rrnF(or G), the genes for 23S, 5S rRNA and tRNA1Asp (F(or G)) are located in that order and separated by intergenic spacers of 93 and 52 base pairs, respectively. A possible hairpin structure, with its center between the 22nd and 23rd base pair downstream from the 3'-end of the tRNA1Asp(F(or G)) gene, followed by a sequence of eight thymidine residues was identified as the transcription termination signal for rrnF(or G). The termination is rho-independent, at least in vitro, and occurs within the region of the contiguous thymidine residues. A possible promoter for a protein gene is present about 50 base pairs downstream from the rrnF(or G) terminator.

Structure of the 5-S ribosomal RNA gene and its adjacent regions in Torulopsis utilis

A DNA segment spanning one repeating unit of ribosomal RNA(rRNA) genes in a yeast strain, Torulopsis utilis, has been cloned on a bacterial plasmid pBR322. The size of the cloned segment was about Mr = 8.0 x 10(6). All of the genes for the four species of rRNA were linked on it, and there was a long spacer between the 5-S and 18-S rRNA coding regions. The nucleotide sequences of the regions flanking the 5-S rRNA gene were determined and compared with those in the corresponding regions of Sacharomyces cerevisiae [Valenzuela, P., Bell, G. I., Masiarz, F. R., DeGennaro, L. J., and Rutter, W. J. (1977) Nature, 267, 641-643; Maxam A. M., Tizard, R., Skryabin, K. G., and Gilbert, W. (1977) Nature, 267, 643-645]. The sequence of the T. utilis 5-S rRNA is identical with that of S. cerevisiae except for two residues at positions 18 and 61. However, its upstream region contained a quite different sequence, and a sequence which showed some homology was only found at positions -21 to -28. The sequences were d(T-G-T-A-A-C-C-T) in T. utilis and d(T-A-T-C-A-C-C-T) in S. cerevisiae. Although the presence of various repeat sequences having the same or opposite directions was noted, these repeats occurred at different positions in the two yeast species. In the downstream region, the common sequence was only seven dT deoxynucleotides, which occurred immediately after the 5-S rRNA coding sequence. Significant direct and inverted repeat sequences were found in T. utilis, but such repeats are not seen in S. cerevisiae.

Cloning of Lac+ BamHI fragment into transposon Tn3 and transposition of the Tn3[lac] element

By use of recombinant DNA techniques, we have inserted the lac+ operon into a transposon (Tn3). We constructed the recombinant in such a way that the essential step in assaying for transposition consisted of screening for bacteria with a thermostable Lac+ phenotype. Our results showed that transposition of the Tn3[lac+] element occurred and that its frequency was derepressed compared to frequencies reported by others for wild-type Tn3 transposition.

Hemolysis determinant common to Escherichia coli hemolytic plasmids of different incompatibility groups

By using cloned deoxyribonucleic acid fragments from the hemolysis determinant of the hemolytic plasmid pHly152 as hybridization probes, a deoxyribonucleic acid segment of about 3.8 megadaltons was identified as a common sequence in several hemolytic (Hly) plasmids of Escherichia coli belonging in four different incompatibility groups. This segment contained the genetic information for the synthesis and secretion of the extracellular toxin alpha-hemolysin of E. coli. With the exception of pSU5, representing a composite plasmid, one part of which seems to be very similar to pHly152, the overall sequence homology of these Hly plasmids with pHly152 seems to be rather restricted. However, the Hly plasmid pSU316 showed sequence homology with pHly152 that did not extend beyond the hemolysis determinant. The two other plasmids, pSU233 and pSU105, also shared homology with pHly152 in the hemolysis determinant as well as in various other parts of this plasmid which did not seem to be directly linked to the hemolysis determinant. This suggests that the hemolysis determinant has spread to presumably unrelated plasmids of E. coli.

Some properties of the ribosomal RNA methyltransferase encoded by ksgA and the polarity of ksgA transcription

The assay for the ksgA-encoded S-adenosylmethionine--6-N',N'-adenosyl (rRNA) dimethyltransferase has been improved; the gel-filtration molecular weight of partially purified enzyme under two different sets of conditions was found to be 55,000 or 26,000 daltons. We have determined methyltransferase activities in strains where ksgA was brought under the control of the mitomycin C-inducible promoter of the colicin E1 gene. Our studies show that ksgA is transcribed counterclockwise on the Escherichia coli chromosome.

Genetic organization and restriction enzyme cleavage map of the ksgA-pdxA region of the Escherichia coli chromosome

Small multicopy plasmids carrying the Escherichia coli genes ksgA and pdxA were constructed by ligation in vitro of an EcoRI restriction fragment from lambda ksg10 (Andrésson and Davies, 1980a) into the EcoRI sites of the ColE1 plasmids RSF2124 and pVH51. Cleavage maps of the plasmids were determined for 21 different restriction enzymes. The ksgA gene was located in a 750 basepairs (bp) region 1,450 bp clockwise of the EcoRI site in folA: pdxA is in a 2,040 bp region immediately clockwise of ksgA.

Molecular cloning of EcoRII endonuclease and methylase genes

The genes for restriction-modification system EcoRII have been cloned from plasmid N3 DNA using RSF2124 as a vector plasmid. The hybrid plasmids designated pFK321 and pFK322 contained a 5.8 megadaltons EcoRI--fragment derived from N3 DNA including the genes for restriction-modification system EcoRII and a gene for resistance to sulfanilamide.

Four sizes of transcript produced by a single sea urchin gene expressed in early embryos

This report concerns a set of sea urchin egg and embryo transcripts complementary to a single-copy region of a cloned DNA fragment (Sp88). Three distinct 16-cell embryo polysomal RNA species were found to hybridize with this fragment. These RNAs are about 1700, 3000, and 4000 nucleotides (nt) in length, and the same species were identified in unfertilized eggs. A significant fraction of all three species of the egg and early embryo transcripts is polyadenylylated. At gastrula stage Sp88 transcripts are almost completely confined to the nucleus [Lev, Z., Thomas, T. L., Lee, A. S., Angerer, R. C., Britten, R. J. & Davidson, E. H. (1980) Dev. Biol, 75, in press]. The Sp88 transcripts of gastrulae are present as a fourth RNA species approximately 5800 nt in length. The four species share a sequence element of cloned DNA fragment that is about 1000 nt long. These RNAs constitute a set of alternative partially overlapping transcripts from the same genomic region.