Isolation of transducing particles of phi-80 bacteriophage that carry different regions of the Escherichia coli genome

Biosynthesis of Arginine and Polyamines

Early investigations on arginine biosynthesis brought to light basic features of metabolic regulation. The most significant advances of the last 10 to 15 years concern the arginine repressor, its structure and mode of action in both E. coli and Salmonella typhimurium, the sequence analysis of all arg structural genes in E. coli and Salmonella typhimurium, the resulting evolutionary inferences, and the dual regulation of the carAB operon. This review provides an overall picture of the pathways, their interconnections, the regulatory circuits involved, and the resulting interferences between arginine and polyamine biosynthesis. Carbamoylphosphate is a precursor common to arginine and the pyrimidines. In both Escherichia coli and Salmonella enterica serovar Typhimurium, it is produced by a single synthetase, carbamoylphosphate synthetase (CPSase), with glutamine as the physiological amino group donor. This situation contrasts with the existence of separate enzymes specific for arginine and pyrimidine biosynthesis in Bacillus subtilis and fungi. Polyamine biosynthesis has been particularly well studied in E. coli, and the cognate genes have been identified in the Salmonella genome as well, including those involved in transport functions. The review summarizes what is known about the enzymes involved in the arginine pathway of E. coli and S. enterica serovar Typhimurium; homologous genes were identified in both organisms, except argF (encoding a supplementary OTCase), which is lacking in Salmonella. Several examples of putative enzyme recruitment (homologous enzymes performing analogous functions) are also presented.

Transsexuality in the rhizosphere: quorum sensing reversibly converts Agrobacterium tumefaciens from phenotypically female to male

Conjugative plasmids generally encode proteins that block the conjugative entry of identical or similar plasmids into the host cell, a phenomenon known as entry exclusion. Here, we demonstrate that two Ti plasmids of Agrobacterium tumefaciens encode robust entry exclusion functions. Two proteins, TrbJ and TrbK, can each mediate entry exclusion and act synergistically. The trbJ and trbK genes are included within the trb operon, which is tightly regulated by the quorum-sensing regulator TraR and the cognate acylhomoserine lactone. In the absence of quorum-sensing signals, these proteins are not significantly expressed, and cells lacking TrbJ and TrbK are efficient Ti plasmid recipients. In the presence of these signals, these strains block the entry of Ti plasmids and instead become efficient conjugal donors.

Characterization of extended-host-range pseudo-T-even bacteriophage Kpp95 isolated on Klebsiella pneumoniae

Kpp95, isolated on Klebsiella pneumoniae, is a bacteriophage with the morphology of T4-type phages and is capable of rapid lysis of host cells. Its double-stranded genomic DNA (ca. 175 kb, estimated by pulsed-field gel electrophoresis) can be cut only by restriction endonucleases with a cleavage site flanked either by A and T or by T, as tested, suggesting that it contains the modified derivative(s) of G and/or C. Over 26 protein bands were visualized upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the virion proteins. N-terminal sequencing indicated that the most abundant band (46 kDa) is the major coat protein (gp23) which has been cleaved from a signal peptide likely with a length similar to that of T4. Phylogenetic analyses based on the sequences of the central region (263 amino acid residues) of gp23 and the full length of gp18 and gp19 placed Kpp95 among the pseudo-T-even subgroup, most closely related to the coliphage JS98. In addition to being able to lyse many extended-spectrum beta-lactamase strains of K. pneumoniae, Kpp95 can lyse Klebsiella oxytoca, Enterobacter agglomerans, and Serratia marcescens cells. Thus, Kpp95 deserves further studies for development as a component of a therapeutic cocktail, owing to its high efficiencies of host lysis plus extended host range.

Transient suppression of F-plasmid incompatibility in a strain of Escherichia coli

The incompatibility between F plasmids is transiently suppressed in Escherichia coli strain CSH54. As a result this strain is able to maintain two F' factors or an F' factor and a mini-F plasmid for considerably longer periods than normal strains. When selective pressure for two markers carried by two separate F's (or an F' and mini-F) is imposed on normal strains, the two plasmids tend to form a cointegrate structure which can be detected genetically by the joint transfer of both the markers upon mating. This does not happen in CSH54; instead, the two plasmids are maintained and transferred independently. Physical evidence for the maintenance of an F' and a mini-F plasmid is provided by agarose gel electrophoresis.

Genetic analysis of Escherichia coli oligopeptide transport mutants

The composition of the outer membrane channels formed by the OmpF and OmpC porins is important in peptide permeation, and elimination of these proteins from the Escherichia coli outer membrane results in a cell in which the primary means for peptide permeation through this cell structure has been lost. E. coli peptide transport mutants which harbor defects in genes other than the ompF/ompC genes have been isolated on the basis of their resistance to toxic tripeptides. The genetic defects carried by these oligopeptide permease-negative (Opp-) strains were found to map in two distinct chromosomal locations. One opp locus was trp linked and mapped to the interval between att phi 80 and galU. Complementation studies with F'123 opp derivatives indicated that this peptide transport locus resembles that characterized in Salmonella typhimurium as a tetracistronic operon (B. G. Hogarth and C. F. Higgins, J. Bacteriol. 153:1548-1551, 1983). The second opp locus, which we have designated oppE, was mapped to the interval between dnaC and hsd at 98.5 min on the E. coli chromosome. The differences in peptide utilization, sensitivity and resistance to toxic peptides, and the L-[U-14C]alanyl-L-alanyl-L-alanine transport properties observed with these Opp-E. coli strains demonstrated that the transport systems encoded by the trp-linked opp genes and by the oppE gene(s) have different substrate preferences. Mutants harboring defects in both peptide transport loci defined in this study would not grow on nutritional peptides except for tri-L-methionine, were totally resistant to toxic peptides, and would not actively transport L-[U-14C]alanyl-L-alanyl-L-alanine.

Physical organization of the metJB component of the Escherichia coli K-12 metJBLF gene cluster

The structures of a series of plaque-forming metJB transducing phage were studied by restriction endonuclease mapping and enzyme activity assay. One of these phage, lambda pmet100, was inactivated by heat shock in the presence of EDTA, and deletion mutants were selected from the survivors. Two of these mutants, lambda pmet100 delta 1 and lambda pmet100 delta 2, were used to confirm the gene order metJ metB when moving clockwise on the linkage map of Escherichia coli K-12. Additional results indicate that the metB gene can be expressed independently of any other component of the met regulon and that the metJ gene also forms a separate transcription unit.

The determination by radiochemical assay of argininosuccinase produced in an Escherichia coli system in vitro

A highly sensitive radiochemical assay used to measure the synthesis and regulation of the product of the argH gene, argininosuccinase, in an Escherichia coli system in vitro is described. With L-[guanidino-14C]argininosuccinic acid as a substrate, and in the presence of excess arginase and urease, 14CO2 is collected in a simply designed micro-vessel. With this method less than 1 nmol of product can be measured in the presence of various concentrations of L-arginine.

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.

Structural studies of lambda transducing bacteriophage carrying bacterial deoxyribonucleic acid from the metBJLF region of the Escherichia coli chromosome

The structures of several lambda dmet and related lambda darg transducing phage were studied by restriction fragment mapping and electron microscopic measurements of homoduplexes and heteroduplexes. A new transducing phage (lambda dmet141), in which metF is the only functional gene of the cluster, was isolated. In contrast, lambda dmet117, which expresses the entire metBJLF cluster, has only 3 kilobases more bacterial deoxyribonucleic acid (DNA) than lambda dmet141. An EcoRI restriction fragment of lambda dmet117, which carries the leftmost 6 kilobases of the bacterial DNA insert, was isolated and shown to contain a functional copy of metB. Small structural differences at the attachment sites of some of the phage were shown to result from different sites of lambda integration in the two parent insertion lysogens.

A new map location for the ilvB locus of Escherichia coli

We isolated, in E. coli K12, new alleles of the ilvB locus, the structural gene for acetolactate synthase isoenzyme I, and showed them to map at or near the ilvB619 site. The map position of the ilvB locus was redetermined because plasmids containing the ilvC-cya portion of the chromosome did not complement mutations at the ilvB locus. Furthermore, diploids for the ilvEDAC genes formed with these plasmids in an ilvHI background facilitated the isolation of the new ilvB alleles. The ilvB locus was remapped and found to be located at 81.5 minutes, between the uhp and dnaA loci. This location was determined by two- and three-point transductional crosses, deletion mapping and complementation with newly isolated plasmids. One of the new alleles of the ilvB gene is a mu-1 insertion. When present in the donor strain, this allele interferes with the linkage of genes flanking the mu-1 insertion, as well as the linkage of genes to either side of the mu-1 insertion.

Isolation and characterization of lambda b221poriCasnA, a plaque-forming specialized transducing phage carrying the origin of replication of the Escherichia coli chromosome

A specialized transducing phage lambda b221poriCasnA has been isolated carrying oriC the origin of chromosomal replication of Escherichia coli. All phage genes required for lytic growth are retained, thus the phage is capable of lytic growth. The presence of the oriC locus confers upon infecting phage DNA the ability to replicate as a plasmid using only host DNA replication functions. The presence of both oriC and ansA markers has allowed the development of a plaque assay for origin function which can be used to identify mutants at these loci. Comparison of restriction endonuclease cleavage sites present on lambda b221proiCasnA DNA to those on its parent, lambda b221 rex::Tn10 suggests the steps involved in the formation of the transducing phage.

Directed integration of an F' plasmid by integrative suppression: isolation of plaque forming lambda transducing phage for the dnaC gene

A new approach for isolation of a plaque forming lambda specialized transducing phage is described. It consists of directed transposition of an F' plasmid into the gal region of a dnaAts galE- Escherichia coli strain by integrative suppression and deletion of the chlD region in order to shorten the distance between the marker of interest on the F' and the prophage serving to prepare an LFT1 lysate. An F' danC+thr+ plasmid was used here and lambdadthr and lambdaddnaC phages were isolated. In addition, lambdapdnaC was obtained from a double lysogen for lambdaddnaC and lambda b2.

Isolation and characterization of specialized lambda transducing bacteriophage carrying the metBJF methionine gene cluster

Secondary attachment site lysogens of Deltaatt(lambda)Deltappc-argECBH strains of Escherichia coli with lambdacI857 integrated into the bfe gene (88 min) were isolated. Of 20 such lysogens examined, 2 produce lysates with transducing phage containing the metBJF gene cluster (87 min). Reintroduction of the ppc-argECBH chromosome segment (which lies between the bfe and met genes) into these strains virtually abolishes the production of met transducing phage. All of the phage examined have lost essential genes from the left arm of the lambda chromosome. Approximately 85% of the phage appear to have the same genetic composition, containing the metBJF gene cluster, but not the closely linked gene cytR, and having lost phage genes G and J. Analytical CsCl density gradient centrifugation of five representatives of this major class of phage shows four of them to have identical densities (lighter than lambda), while the fifth cannot be resolved from lambda. The four apparently identical phage were isolated from three separate lysates, which suggests the existence of preferred sites for illegitimate recombination on the bacterial and phage chromosomes. Three specialized transducing phage that carry cytR in addition to metB, metJ, and metF have also been studied. Each of these viruses has a different amount of phage deoxyribonucleic acid. Two of them have less deoxyribonucleic acid than lambda, whereas the third has about the same amount. The metB, metF, and cytR genes of the transducing phage have been shown to function in vivo. The phage-borne metB and metF genes are subject to metJ-mediated repression.

Metabolism of arginine-specific messenger ribonucleic acid in Escherichia coli K-12

Ribonucleic acid-deoxyribonucleic acid (RNA-DNA) hybridization was employed for the determination of the level of messenger RNA (mRNA) transcribed from seven of the nine genes of the arginine regulon of Escherichia coli K-12. The quantity of RNA complexing with each of the separated DNA strands of the argA, argF, argE, and argCBH operons carried on specialized transducing phages was measured. The derepressed:repressed ratio of mRNA formed in vivo was found to vary between about 3 and 4 when measured by hybridization to DNA isolated from specialized transducing phages carrying the argA, argE, argCBH, argF, and argI operons.

Genetics of sensitivity of Salmonella species to colicin M and bacteriophages T5, T1, and ES18

Nearly all of 62 strains of Salmonella paratyphi B were sensitive to colicin M and phage T5 but resistant to phages T1 and ES18 and to colicin B. All tested S. typhimurium strains were resistant to colicin M and phage T5, and many were sensitive to phage ES18. A rough S. typhimurium LT2 strain given the tonA region of Escherichia coli or S. paratyphi B became sensitive to colicin M and phage T5. We infer that the tonA allele of S. paratyphi B, like that of E. coli, determines an outer membrane protein that adsorbs T5 and colicin M but not phage ES18, whereas the S. typhimurium allele determines a protein able to adsorb only ES18. The partial T1 sensitivity of a rough LT2 strain with a tonA allele from E. coli or S. paratyphi B and also the tonB(+) phentotype of an E. coli B trp-tonB Delta mutant carrying an F' trp of LT2 origin showed that S. typhimurium LT2 has a tonB allele like that of E. coli with respect to determination of sensitivity to colicins and phage T1. Rough S. paratyphi B, although T5 sensitive, remained resistant to T1 even when given F' tonB(+) of E. coli origin. Classes of Salmonella mutants selected as resistant to colicin M included: T5-resistant mutants, probably tonA(-); mutants unchanged except for M resistance, perhaps tolerant; and Exb(+) mutants, producing a colicin inhibitor (presumably enterochelin). Some Exb(+) mutants were resistant to a bacteriocin inactive on E. coli but active on all tested S. paratyphi B and S. typhimurium strains (and on nearly all other tested Salmonella). A survey showed sensitivity to colicin M in several other species of Salmonella.

In vitro transcription of the Escherichia coli K-12 argA, argE, and argCBH operons

Deoxyribonucleic acid isolated from argA and argECBH transducing phages was utilized to study the in vitro synthesis of argA, argE, and argCBH messenger ribonucleic acid. The specific regulation of these operons by the arginine holorepressor was demonstrated, providing evidence that the majority, if not all, of the control of these operons is exercised at the transcriptional level. Data are presented which indicate that the arginine holorepressor functions by binding to the operator region and concomitantly prevents the binding of ribonucleic acid polymerase to the corresponding promoter region.

Role of dnaB43 in F'-plasmid incompatibility

In order to perform complementation tests with mutations of DNA replication of F'-plasmids incompatibility must overcome. We report out in ability to duplicate the results presented by Palchoudhury and Iyer (1971) and Bezanson and Iyer (1975) who have claimed to demonstrate the autonomous replication two incompatible F'-plasmids in a strain carrying the temperature sensitive dna B43 allele. In addition, we describe experiments designed to measured complementation using transient heterozygotes and compatible plasmids. Assessment of our data and those of others in the light of a recent report by Uhlin and Nordström (1975) suggests that new approaches will have to be developed for the successful employment of complementation analysis in F-plasmid genetics.

The use of specialised transducing phages in the amplification of enzyme production

Two types of lambdatrp phages have been used as model systems to investigate ways of optimising the expression of bacterial genes from transducing phage genomes. Excellent yields of trp enzymes were achieved by infecting a trpR- host with Q- or Q-S- derivatives of lambdatrpAM1, which expresses its trp genese exclusively from the trp promoter. The five trp geneproducts constituted more than 50% of the total soluble protein of infected cells under these conditions, and an even higher proportion of the protein synthesized after infection. In a trpR+ host, phage DNA replication was easily able to override tryptophan-mediated repression by titration of the trp promoter were equally productive, while having the advantage of being much simpler to construct and propagate. lambdatrp phages lacking the trp promoter were used to investigate ways of optimising gene expression initiated at the phage promoter, PL. Though very powerful, the latter promoter is more difficult to harness then the trp promoter. Derepression of transcription from PL by the use of cro- mutations is accompanied by poor replication of transducing phage DNA. Attempts to circumvent this difficulty using virulent of cro,cII double mutants have not been successful. Nevertheless, cells infected with a lambdatrp phage expressing its trp genes exclusively from PL made up to 16 per cent of their protein as trp gene-products.

Isolation and characterization of phi80dgal transducing phages that carry gal operator-promoter insertion mutations

phi80dgal transducing bacteriophages have been isolated by the F-fusion technique of Press et al. (1971) and gal-operator-promoter insertion mutations have been introduced by homogenate formation. Five different phi80dgal isolates have been studied in more detail. One of the phi80 phages transduces the gal operon and gene aroG as well as at least part of the trp-operon; the gal operon of another phi80dgal transducing phage is inverted with respect to the phi80dgal sequences. Heteroduplex DNA mapping indicates that one of the phi80dgal isolates in addition to the gal operon and a portion of the adjacent chromosomal region carries an IS2-element which is derived from the F'gal episome. The isolated phi80dgal phages may be utilized for preparing pure gal mRNA and insertion-RNA as well as pure gal operon DNA.

Fusion of two F-prime factors in Escherichia coli studied by electron microscope heteroduplex analysis

A fused F prime factor was obtained from a mating of a recA donor carrying an F'- factor containing the genes metBJF, ppc and argECBH (KLF5) with a recA recipient carrying an F' factor containing att80, trp and lac (f155). lysogenization of this fused F-prime factor with gammacI857hphi80 phage followed by thermoinduction produced the transducing phages phi80 dmetBJF and phi80 dppcargECBH. This kind of fusion provides a general procedure for the construction of transducing phages carrying genes from different regions of the E. coli genome. To understand the mechanism of this fusion, the parental F prime factors (F155 and KLF5) were analyzed by the electron microscope heteroduplex technique. F155 has a length of 176 +/- 3 kilobases including two substitutions. The F sequence 0 F-2.8 F has been substituted by 53 kb of chromosomal DNA including the lac operon and the F sequences 8.5 F-16.3 F has been substituted by 27 kb of a chromosome sequence including att80 and the trp operon KLF5 contains 221 +/- 4 kilobases of DNA (molecular weight, 148 megadaltons). It contains complete F and the segment of the E. coli chromosome from polA to rif. The F sequence 2.8 F-8.5 F known to be involved in F specific recombination in recA+ and recA backgrounds occurs twice on KLF5, once at each of the junctions of F DNA with chromosomal DNA. The population of closed circular plasmid molecules extracted from KLF5-containing strains is heterogeneous. It is proposed that this heterogeneity is due to intramolecular recombination events occurring in KLF5 between the duplicated 2.8 F-8.5 F sequences. Such recombination can account for the genetic instability of KLF5 observed in both recA+ and recA hosts. The F sequence 2.8 F-8.5 (also called gammadelta) is one of the characterized integration sequences on F. A model for the fusion of the parental F prime factors is proposed in which recombination between gammadelta sequences brings att80 close to the metBJF genes. This is followed by a deletion of an F' lac factor. The resulting fused F' factor still carries two gammadelta sequences and is therefore expected to be unstable. The closed circular molecules isolated from the fused F' containing strains show two different sizes of molecules. Genetic and physical analyses of these molecules are in agreement with the predicted instability of the fused F' factor and the existance of the gammadelta sequence in the phi80 dmet phages isolated from fused F' and previously analyzed by the electron microscope heteroduplex technique.

Specialized transduction of D-serine deaminase genes: formation of lysogens that yield high lambda-d dsd/lambda ratios and formation of a dimeric lambda-d dsd

We have obtained two classes of double lysogens that on induction yield higher titers of lambda-d dsd transducing phage than of helper phage. One class was obtained by lysogenization of strain EM6116 (dsddelta attlambdadelta HfrC) with lambda-dsd type 2 (dsdC+ dsdO+ dsdA+, head-tail substitution). In the absence of either a normal attlambda or the homology of a chromosomal dsd region, the transducing phage integrated at other sites, at least one of which, in strain EM6177, is near the origin of HfrC. On induction, strain EM6177 yields a phage burst of 20 to 50 with a lambdadsd:lambda ratio of 10(4):1. The asnychronously high yield of lambda dsd is attributed to an efficiency of excision greater than that of lambda. The other class was obtained by lysogenization of strain EM1407 (dsdA attlambda+) with lambda-dsd type 2 (dsdO6 dsdA, partial deletion of dsdC). The DNA of mature lambda-dsd type 2 is a complete dimer. It lacks nearly all the phage late genes and b2 and carries about five bacterial genes. It could not be packaged as a monomer but is just within the packaging size limit as a dimer. Models for the derivation of these lambda dsd phages and the high-yielding lysogens are presented.

The construction in vitro of transducing derivatives of phage lambda

Methods are described for the construction of plaque-forming, transducing derivatives of phage lambda, using appropirate receptor genomes and fragments of DNA generated by the restriction enzymes endo R.EcoRI and endo R.HindIII. The general properties of the transducing derivatives are described and discussed. Plaque-forming phages carrying the E. coli trp, his, cysB, thyA, supD, supE, sup F, hsd, tna and lig genes have been isolated.

Isolation and characterization of the specialized transducing bacteriophages phi80dargF and lambdah80cI857 dargF: specific cleavage of arginine transducing deoxyribonucleic acid by the endonucleases EcoRI and SmaR

The directed transposition of argF to the tonB locus of the Escherichia coli chromosome and the subsequent isolation of the specialized transducing phage phi80dargF is described. The structure of this phage has been has been determined. A hybrid lambdah80cI857dargF phage has been constructed. Deoxyribonucleic acid isolated from these and their parent bacteriophages has been specifically cleaved by the endonucleases EcoRI and SmaR; the unique deoxyribonucleic acid fragments thus obtained have been resolved and analyzed by electrophoresis in agarose gel.

Expression of the argA gene carried by a defective lambda bacteriophage of Escherichia coli

Evidence is presented that the increase in specific activity of N-acetylglutamate synthase observed upon heat induction of Escherichia coli (lambdadargA) is primarily due to a gene dosage effect.

In vitro synthesis and repression of argininosuccinase in Escherichia coli K12; partial purification of the arginine repressor

Phi80dargECBH DNA has been used to direct cell-free synthesis of argininosuccinase, the argH gene product in Escherichia coli K12. In vitro enzyme synthesis is sensitive to repression by partially purified preparations from an argR+ strain but not by corresponding preparations from an argR- strain. Using DNA-cellulose chromatography, approximately seventyfold purification of repressor has been obtained. The partially purified preparation represses argininosuccinase synthesis but has no effect on beta-galactosidase synthesis.

Isolation and characterization of lambdadargECBH transducing phages and heteroduplex analysis of the argECBH cluster

Transducing lambda bacteriophages have been isolated which carry the divergently transcribed argECBH operon of E. coli K12 and various portions of the adjacent ppc and bfe chromosomal regions. They were recovered from lysates prepared by the procedure of Schrenk and Weisberg using a Ppc+ Arg+ Bfe+ strain carrying a deletion of the usual attachment site of lambda. Heteroduplex DNA mapping of these lumbdadarg and of the phi 80 darg isolated by B. Konrad indicates that the two kinds of phages carry the arg cluster in opposite orientations, a situation favorable for the isolation of argECBH DNA. A physical map of the ppc argECBH bfe region including 2 unusual attachment sites of lambda has been constructed. The localization of the end points of certain arg deletions provides a useful reference framework for the currently pursued mapping of mutations affecting the control of divergent transcription and for the location of restriction enzyme cleavage sites in the arg region.

cis-Dominant, transfer-deficient mutants of the Escherichia coli K-12 F sex factor

Rare conjugational progeny formed by crossing each of five Hfr strains with a recA-F- strain have been characterized. Selection was made for a proximal Hfr marker, taking strict precautions to prevent transfer of recA+ to the zygotes. Most of the progeny were found to be F' strains containing deletion mutant plasmids. With two exceptions, these mutant plasmids have lost all of the tra genes, which are required to confer conjugational donor ability upon a host. In addition, all but the exceptional mutant plasmids were found to be very poorly transmissible from transient heterozygotes which also contain a wild-type F' plasmid. The poor transmissibility is a cis-dominant transfer-defective phenotype which may result from deletion of all or part of the origin of transfer replication (ori), or of a gene determining a cis-acting protein. The two exceptional mutant plasmids may carry short deletions of some of the tra genes or polar tra mutations. The remaining progeny were nonmutant F' strains and F- strains. The frequency with which the F- strains were recovered permits us to estimate that the maximum amount of recombination possible in a recA56 zygote is 10(-6) that of a recA+ zygote.

Genetic mapping of a mutation that causes ribonucleases III deficiency in Escherichia coli

the mutation that causes ribonuclease III (RNase III) deficiency in strain AB301-105 of Kindler et al. (1973) has been mapped by use of F' merodiploids, Hfr matings, and P1 transduction. This mutation, rnc-105, lies close to nadB, near 49 min on the genetic map of Escherichia coli. The rnc-105 mutation has been transferred from its original genetic background by transduction and conjugation, and these new strains have the same defects in ribonucleic acid processing reported previously for AB301-105. Strains that carry rnc-105 grow more slowly than parental rnc+ strains, but the difference in growth rate seems to depend on the genetic background of each strain. Bacteriophage T7 grows about equally well in RNase III+ and III- female strains of E. coli, even though the specific cuts that RNase III makes in T7 ribonucleic acid are not made in the RNase III- strains. A low-phosphate defined medium in which most E. coli strains seem to grow well was developed. This medium is equally useful for labeling ribonucleic acids with 32PO4 and as a selective medium for genetic manipulations. It was used to determine the growth requirements of strain AB301-105, which are biotin and succinate in addition to the methionine and histidine requirements of the parental strain. The biotin mutation lies near the position expected from known mutations of E. coli, but the succinate mutation apparently does not. The possibility that the succinate requirement could be due to the RNase III deficiency is discussed. A uraP mutation was isolated for use in transferring rnc-105 between strains by conjugation. It lies near 47 min, somewhat removed from the commonly accepted position for uraP.

Isolation of a hybrid F' factor-carrying Escherichia coli lactose region and Salmonella typhimurium histidine region, F42-400 (F' ts114 lac+, his+): its partial characterization and behavior in Salmonella typhimurium

Episome F' ts114 lac+ (F42-114) was transferred into Salmonella typhimurium carrying an F'his+ (FS400) episome, and fused episome F' ts114 lac+, his+ (F42-400) was obtained. Episome F42-400 could be transferred to S. typhimurium, Escherichia coli and Klebsiella pneumoniae. Identification of the episome was based on: (i) temperature sensitivity of the Lac+ and His+ phenotypes; (ii) the fact that F- segregants, obtained after temperature curing or acridine orange curing, were simultaneously Lac- and His-; and (iii) linkage of lac+ with his+ in episomal transfers to E. coli and S. typhimurium. The frequency of episome transfer was influenced by the genotype of the donor. Plasmid LT2, prevalent in S. typhimurium LT2 strains, was suggested to be responsible for the low fertility of S. typhimurium donors. Episome F42-400 was capable of chromosome mobilization, and the extent of chromosome mobilization was not influenced by the presence or absence of the histidine region on the donor chromosome. Growth in a defined medium with acridine orange was able to cure F42-400. The frequency of curing was increased (the frequency of His+ cells was 0.0001%) if the cells were grown at 40 C in the presence of acridine orange. Selection for temperature-resistant Lac+, His+ derivatives in a strain without histidine deletion yielded Hfr strains. However, similar and stronger selections in strains without the chromosomal histidine region failed to yield Hfr strains. Our inability to obtain Hfr's in strains without the chromosomal histidine region was explained by assuming that the episome F42-400 has lost the F sites involved in integration into the S. typhimurium chromosome.

A simple method for making new transducing lines of coliphage lambda

A variety of novel transducing lines of phage lambda can be obtained by induction of a mixed culture of abnormal lysogens. Such a culture is simply made by mass lysogenization of a host lacking the normal prophage attachment site.

Plasmid mutations affecting self-maintenance and host growth in Escherichia coli

As reported in the accompanying paper, a number of mutants of the ColVBtrp plasmid that can not be maintained stably in the host cell of Escherichia coli have been isolated. Each of the mutated plasmids has been transferred to an isogenic Col minus strain, and the resulting Col+ strains were studied to examine the effects of plasmid mutations on some properties of the host bacteria. Many of the strains harboring a mutated plasmid were thus found to be temperature sensitive; they failed to grow and divide normally at high temperatures. Some of them formed "filaments" under these conditions. These abnormal growth characteristics were accompanied by an increased susceptibility to sodium deoxycholate and methylene blue, suggesting that the cytoplasmic membrane has been altered. Moreover, studies of temperature-independent revertants obtained from two of these temperature-sensitive Col+ strains suggested that a single mutation on the plasmid is responsible for the pleiotropic effects exerted on the host cell. The bearing of these findings on the mode of replication and segregated of stringent-type plasmids such as ColVBtrp in the host bacteria is discussed.

Isolation and characterization of lambda transducing bacteriophages for the su1+ (supD minus) amber suppressor of Escherichia coli

Specialized lambda transducing phages for the sul+ (supD-) amber suppressor in Escherichia coli K-12 have been isolated, using a secondary site lambda-cI857 lysogen in which we have shown the prophage to be closely linked to sul+.sul+ transducing particles were detected frequently, at 10-5 per plaque-forming unit, in lysates prepared from the secondary-site lysogens. High-frequency transducing lysates were obtained from several independently isolated sul+ transductants and were analyzed by CsCl equilibrium density gradient centrifugation. The transducing phages are defective; marker rescue analysis indicates that the lambda-N gene is not present. In lambda-cI857DELTANdSul+, a bio-type transducing phage, the genes specifying recombination and excision functions have been replaced by bacterial deoxyribonucleic acid.

Isoleucine and valine metabolism in Escherichia coli K-12: detection and measurement of ilv-specific messenger ribonucleic acid

Ribonucleic acid-deoxyribonucleic acid (RNA-DNA) hybridization was employed for the determination of messenger RNA transcribed from the ilv gene cluster of Escherichia coli K-12. Strains with derepressed levels of the isoleucine and valine biosynthetic enzymes owing to linked or unlinked genetic lesions were found to exhibit ilv messenger RNA levels from 1.5- to 4-fold higher than did their isogenic parents. When grown under conditions that specifically repressed the synthesis of isoleucine- and valine-forming enzymes, most strains exhibited drastically reduced ilv messenger RNA levels. Hybridization performed with the separated strands of ilv DNA showed that all the ilv genes are transcribed from the same strand, the "l strand" of lambdaphi80CI857St68dilv DNA. Sucrose gradient analyses of RNA extracted from cells starved for isoleucine, valine, or leucine resulted in the detection of at least two distinct types of ilv messenger RNA.

Complementation between different mutations in the ilvA gene of Escherichia coli K-12

An ilvA mutation carried by a ø80i(lambda)dilv transducing phage complemented some ilvA mutations and did not complement others. Complementation was accompanied by appearance of threonine deaminase activity in vivo. These results divided the ilvA mutations into two sets which formerly appeared to define two cistrons.

Isolation of a specialized transducing bacteriophage lambda carrying the polC locus of Escherichia coli

We have isolated a specialized transducing phage carrying the polC locus of E. coli K-12. A strain of E. coli lacking the lambda attachment site was infected with bacteriophage lambda. Lysogens carrying lambda at the tonA locus were isolated by selecting lambda-immune, T5-resistant strains. Transducing phages of dapC, dapD and polC, which map within 0.2 min of tonA, were obtained in lysates prepared from two of the lysogens. The isolated phage, lambdadpolC, is defective but can transduce four different polC temperature-sensitive mutants. After lysogenation with the transducing phage, DNA polymerase III activity is restored to normal levels in extracts of a polC strain lacking polymerase III activity. However, attempts to obtain increased levels of DNA polymerase III in extracts of induced lysogens carrying lambdadpolC have been unsuccessful.

Isolation of a specialized lambda transducing bacteriophage carrying the beta subunit gene for Escherichia coli ribonucleic acid polymerase

A heat-inducible lysis-defective lambda prophage has been integrated directly into the E. coli chromosome at a site (bfe) very closely linked to the ribonucleic acid polymerase mutation rif(d), a dominant rifampin resistance allele. This unusual lysogen has facilitated the isolation of specialized transducing phages conferring rifampin resistance to sensitive cells, and carrying at least the beta subunit gene of RNA polymerase in intact form.

Rapid mapping of conditional and auxotrophic mutations in Escherichia coli K-12

The approximate genetic map locations of auxotrophic and conditional lethal mutations of Escherichia coli can be rapidly determined with replica plating techniques. A set of patches of 15 streptomycin-sensitive (Str(S)) Hfr strains with points of origin distributed around the map is replica plated onto a recombinant-selective plate with a lawn of Str(R) cells which carry an unmapped mutation. The map interval defined by the Hfr points of origin which are closest to the mutant locus is seen by the presence or absence of heavy patches of recombinants produced by transfer of early wild-type genes from the Hfrs. An alternative method is to replicate patches of different mutant strains (100 per plate) onto Hfr lawns; in this case more than 1,000 different mutants can be mapped in a single experiment in a few days. In this way, many types of mutations with similar phenotypes can be grouped as to approximate location on the genetic map. For ordering mutations within groups, the same replica plating methods can be used to cross F-prime derivatives of mutants with other mutants of the same group. Relative merits of these and other mapping methods of E. coli are discussed.

Isolation of transducing bacteriophages for the histidine and isoleucine-valine operons in Escherichia coli K-12

In vitro studies have been of great value in elucidating the mechanism of the regulation of several bacterial operons. To obtain a deoxyribonucleic acid preparation enriched for the histidine (his) and for the isoleucine-valine (ilv) operons, we have isolated bacteriophages carrying the his and the ilv regions of the Escherichia coli chromosome. Transposition of the his operon to a site close to the att80 region of the E. coli chromosome has been carried out selecting for integration of a temperature-sensitive F'his(+) in the tonB locus. This transposed strain has been lysogenized with phi80i(lambda). Upon induction of the lysogen, His(+) transductants have been isolated, which, on further induction give rise to HFT (high frequency of transduction) lysates. Preliminary characterization of the transducing phage is reported. The ilv operon, carried on an F' particle, has been fused to an episome carrying the att80 region. The fused episome has been lysogenized with phi80i lambdat68. Upon induction of the lysogen, Ilv(+) transductants have been isolated which on further induction give rise to HFT lysates.

Characterization by electron microscopy of fused F-prime factors in Escherichia coli

During previous attempts to find mutants in which incompatibility between two F-prime (F') factors of E. coli is abolished, we found that two F' factors harbored in the same cell occasionally recombined to form a single genetic unit. Thus, a fused F'trp(+)arg(+) factor was obtained from a mating of a strain carrying recA F'trp(+) with a strain carrying recA F'arg(+). In the present paper physical fusion of the two F' factors, inferred from genetic studies, is confirmed by electron microscopy. F DNA was extracted, after detergent lysis, from four fused F' strains: the parental F'trp(+) and F'arg(+) strains and three F(+) strains. This supercoiled DNA was separated on ethidium bromide-cesium chloride gradients and converted to the open circular from before electron microscopy. The contour lengths in mum of the various DNA preparations were: F'trp(+), 59.4; F'arg(+), 33.2; the four F'trp(+)arg(+) factors, 38.5, 39.6, 63.2, and 73.5: the three F factors, 31.1, 31.1, and 31.0. Thus, different fused F' factors formed from the same parental F' factors vary in length, but are shorter than the sum of the parental F' factors.