Isolation and characterization of new sus (amber) mutants of bacteriophage lambda

Complementation Studies of Bacteriophage λ O Amber Mutants by Allelic Forms of O Expressed from Plasmid, and O-P Interaction Phenotypes

λ genes O and P are required for replication initiation from the bacteriophage λ origin site, oriλ, located within gene O. Questions have persisted for years about whether O-defects can indeed be complemented in trans. We show the effect of original null mutations in O and the influence of four origin mutations (three are in-frame deletions and one is a point mutation) on complementation. This is the first demonstration that O proteins with internal deletions can complement for O activity, and that expression of the N-terminal portion of gene P can completely prevent O complementation. We show that O-P co-expression can limit the lethal effect of P on cell growth. We explore the influence of the contiguous small RNA OOP on O complementation and P-lethality.

Host responses influence on the induction of lambda prophage

Inactivation of bacteriophage lambda CI repressor leads almost exclusively to lytic development. Prophage induction can be initiated either by DNA damage or by heat treatment of a temperature-sensitive repressor. These two treatments also cause a concurrent activation of either the host SOS or heat-shock stress responses respectively. We studied the effects of these two methods of induction on the lytic pathway by monitoring the activation of different lambda promoters, and found that the lambda genetic network co-ordinates information from the host stress response networks. Our results show that the function of the CII transcriptional activator, which facilitates the lysogenic developmental pathway, is not observed following either method of induction. Mutations in the cro gene restore the CII function irrespective of the induction method. Deletion of the heat-shock protease gene ftsH can also restore CII function following heat induction but not following SOS induction. Our findings highlight the importance of the elimination of CII function during induction as a way to ensure an efficient lytic outcome. We also show that, despite the common inhibitory effect on CII function, there are significant differences in the heat- and SOS-induced pathways leading to the lytic cascade.

The carboxy-terminal 14 amino acids of phage lambda N protein are dispensable for transcription antitermination

The analogous N proteins encoded by lambdoid bacteriophages lambda, 21, and 22 are very different in amino acid sequence, except at their carboxy-terminal ends. Since N lambda remains functional despite the deletion of most of its terminal region of homology to N21, that region of homology cannot represent a region of conserved function.

Involvement of the htpR gene product of Escherichia coli in phage lambda development

Growth of phage lambda at high temperature requires a functional htpR host gene. The stages of the phage growth cycle shown to be dependent on htpR gene function include prophage excision and particle morphogenesis. Two types of morphogenetic abnormalities have been detected. One is a defect in phage tail assembly that results from a deficiency in tail fibers even though gpJ is produced. The severity of this defect is phage-strain specific. The second morphogenetic defect is less clearly defined, but results in formation of aberrant phage head structures. These abnormalities in lambda reproduction are presumed to be caused by the absence in htpR mutant host cells at high temperature of one or more of the heat-shock proteins of Escherichia coli whose synthesis is known to be regulated by the htpR gene.

A third defective lambdoid prophage of Escherichia coli K12 defined by the lambda derivative, lambdaqin111

We describe the isolation and characterization of a new Q-independent substitution mutant of lambda, lambdaqin111, which differs from other characterized Q-independent lambda phages. This mutant defines a new lambda-like prophage in the bacterial chromosome, as seen by homologous recombination between lambdaqin111 and the host DNA and by DNA/DNA hybridization methods. Genetic and electron microscopy data show that this new prophage carries, at least, genes analogous to Q-S-R of lambda and also a cos site functionally identical to lambda cos. It is located near 34 min on the Escherichia coli K12 map, i.e. in the same region but at a different site from the defective Rac prophage.

Analysis of nutR: a region of phage lambda required for antitermination of transcription

The N gene product of coliphage lambda acts with host factors (Nus) through sites (nut) to render subsequent downstream transcription resistant to a variety of termination signals. These sites, nutR and nutL, are downstream, respectively, from the early promoters PR and PL. Thus a complicated set of molecular interactions are likely to occur at the nut sites. We have selected mutations in the nutR region that reduce the effectiveness of pN in altering transcription initiating at the PR promoter. DNA sequence analysis of three independently selected mutations revealed, in each case, a deletion of a single base pair in the cro gene. Consideration of the effect of such mutations on the extension of translation of cro message into the adjacent downstream nut region led to the identification of a consensus sequence CGCTCT(T)TAA that appears to play a role in the recognition of a host factor, possibly the NusA protein.

Induction of mutations in bacteriophage T7 by gamma-rays: no influence of the SOS repair pathway

Under conditions where the reversion of an amber mutant of bacteriophage lambda by gamma-rays is enhanced by subjecting the irradiated phage to SOS repair, gamma-ray-induced reversion of two T7 ambers is not influenced by this error-prone bacterial repair system. The survival of T7 gamma-irradiated under anoxic conditions is somewhat enhanced by SOS repair, whereas the survival of phage irradiated under oxygen is not affected.

The N protein of bacteriophage lambda, defined by its DNA sequence, is highly basic

Nucleotide sequence has been determined for the restriction fragments and cloned DNA from the pL-N-tL1 region of bacteriophage lambda. A unique reading frame for the N gene is defined by the absence of natural nonsense codons and by the presence of seven nonsense codons generated by mutations in N. This reading frame is initiated at two alternative ATG codons, the second of which is probably the in vivo translation start. Reading is stopped at a single TAG codon. The protein coded is therefore 133 or, more probably, 107 amino acids long, rich in lysine, arginine and proline.

A comprehensive molecular map of bacteriophage lambda

Physical and genetic mapping of deletion mutations has been correlated with the available molecular sizes of the lambda gene products and the DNA base sequence to construct a comprehensive molecular map of the phage lambda genome. The physical length of the DNA making up the left arm from the cos site through gene J is not sufficient to account in a nonoverlapping manner for all the proteins of the sizes reported to be coded, especially in the Nu1--C region. In the right arm all the coding capacity has not been accounted for, and it appears to be oversaturated only in the gam-ral region. The positions of several IS and Tn elements, and of restriction endonuclease cleavage sites are specified.

Mini-muduction: a new mode of gene transfer mediated by mini-mu

We compared the transducing properties of Mucts62 and Mucts62/mini-Mu lysates, using Mu immune and non immune Recqnd recA recipient strains. The Mu/mini-Mu lysates transduced all bacterial markers tested 10 times more efficiently than the Mucts62 lysates in Rec + recipients. Most of the transductants obtained after infection with the Mu/mini-Mu lysates result from the substitution of the mutated gene of the recipient by the wild type allele from the donor, most probably carried on the gigantic variable end linked to the mini-Mu genome. Moreover the Mu/mini-Mu lysates gave a new type of Rec-independent transduction that we called mini-muduction. Mini-muduction requires the activity of Mu gene A and provides transductants which carry the transduced marker surrounded by two mini-Mu genomes similarly oriented, and inserted at random location in the recipient chromosome. The mini-Mu/transduced DNA/mini-Mu structures are able to transpose spontaneously, for instance into a transmissible plasmid, in the presence of Mu gene A product.

Stimulation of deletions in the Escherichia coli chromosome by partially induced Mucts62 prophages

Deletion of bacterial DNA fragments is stimulated in induced Mucts62 lysogens. The host genes located proximally to the prophage are more frequently lost than those which are unlinked to the Mu genome. Genes located on either side of a Mu genome are deleted in the same manner. Like the other Mu-induced rearrangements, this process is recA independent and requires the participation of Mu DNA, as indicated by the fact that a phage genome always replaces the deleted genes. Data are presented which strongly suggest that both ends of the Mu genome are involved in deletion formation.

Specificity of polarity suppression in E. coli: correction of defects in gene N, but not in gene Q, of phage lambda

The bacterial mutation psuA1, known as (suA) a polarity suppressor, partially relieves all N defects in bacteriophage lambda growth. No evidence is found that psuA1 relieves Q defects in lambda growth. Specific mechanisms of action by the N and Q gene products are discussed. The psuA1 mutation was also found to suppress IS1 type but not IS2 type insertion mutations in lambda.

Suppression of polarity of insertion mutations in the gal operon and N mutations in bacteriophage lambda

Bacterial mutations (psuA and psu) known for their ability to suppress the polarity on nonsense mutations are shown to suppress the polarity of certain insertion mutations in the gal operon. The short insertion, IS1 (800 nucleotide pairs), is about 15 to 50% suppressed, whereas longer insertions, IS2 (1,400 nucleotide pairs), and IS3 (1,200 nucleotide pairs), are not. Some of the polarity suppressor mutations (psu-1, psu-2, and psu-3) are at least partially permissive for N-gene mutations (N7 and N53) of bacteriophage lambda, suggesting a relationship between natural and mutational polar signals. That this relationship may be complex is indicated by the fact that other suppressor mutations, effective in suppressing nonsense or insertion polarity, fail entirely to permit the growth of lambda N mutants.

Isolation of a strong suppressor of nonsense mutations in Bacillus subtilis

By treatment of Bacillus subtilis MO-101-P spoA- met thr- su- with ethyl methanesulfonate, a strong suppressor strain of nonsense mutations, B. subtilis MO-101-P spoA- [met-]+thr- su+44, was isolated. This strain does not suppress phage phi 29 mutant susB47, selected on a B. subtilis strain containing the su+3 suppressor isolated by Georgopoulos. A revertant from this mutant, susB610, was isolated, being suppressed by both the su+3 and su+44 suppressor strains. The efficiency of suppression by strain su+44 is about 50%. The experiments shown in this paper suggest that strain su+44 contains an amber and strain su+3 an ochre suppressor.

U.V. induced enhancement of recombination among lambda bacteriophages: relation with replication of irradiated DNA

Experimental results are reported showing the dependence of the U.V. induced enhancement of recombinants on the presence of the functional O gene product. This fact is tentatively interpreted as a replication dependence of the U.V. induced recombination.

Bacterial mutants able to partly suppress the effect of N mutations in bacteriophage λ

A method is described whereby bacterial mutants (sun) may be selected which are able to specifically suppress mutations in the N gene of bacteriophage lambda. The sun mutations seem to be allelic to suA mutations, which suppress the polarity of nonsense codons, since suA mutants have all of the properties of sun mutants and both are genetically linked to the ilv gene. In the light of these experiments and recent data by others, models originally suggested to explain polarity in bacterial operons, are discussed with regard to their possible relevance to the mechanism of N action.

Model for the enchancement of lambde-gal integration into partially induced Mu-1 lysogens

Temperate phage Mu-1, which is able to integrate at random in its host chromosome, is also able to mediate integration of other circular deoxyribonucleic acid, as a lambda-gal mutant unable to integrate by itself. After mixed infection with lambda-gal and Mucplus, galplus transductants are recovered that have the lambda-gal integrated in any circular permutation, sandwiched between two complete Mu genomes in the same orientation, the whole Mu-lambda-gal-Mu structure being found at any location in the bacterial chromosome. Here we show that such a lambda-gal can integrate in an induced Mu lysogen. In this case the lambda-gal is again in any circular permutation, between two Mu in the same orientation, but it is always located at the site of the original Mu prophage, and the two surrounding Mu have always the same genotype as the original Mu prophage. Active Mu replication functions are not essential for that process to occur. This suggests that bacterial replication may generate two Mu copies that in some way can regenerate a Mu attachment site that recombines with the lambda-gal. A model is presented that accounts for these observations, may be helpful for understanding some complex features of Mu development, and may possibly offer a basis for explaining spontaneous duplications.

Isolation of a suppressor host bacterium in Staphylococcus aureus

A bacterial mutant of Staphylococcus aureus NCTC 8325 has been isolated which has the properties of a suppressor host mutant. The mutant was isolated as a one-step phenotypic revertant to wild type of a strain containing mutations in two unlinked markers concerned with metabolism of lactose via the phosphoenol pyruvate-dependent phosphotransferase system. The revertant (called sup1(+)) has been used to isolate seventy conditional lethal mutants of the phage O11. The phage mutants, which plate on sup1(+) but not on the original 8325 strain, have been assigned by complementation studies into 10 groups. It is probable that this technique for the isolation of suppressor hosts would be applicable to other Staphylococcus strains.

Isolation of plaque-forming, galactose-transducing strains of phage lambda

Plaque-forming, galactose-transducing lambda strains have been isolated from lysogens in which bacterial genes have been removed from between the galactose operon and the prophage by deletion mutation.-A second class has been isolated starting with a lysogenic strain which carries a deletion of the genes to the right of the galactose operon and part of the prophage. This strain was lysogenized with a second lambda phage to yield a lysogen from which galactose-transducing, plaque-forming phages were obtained. These plaque-forming phages were found to be genetically unstable, due to a duplication of part of the lambda chromosome. The genetic instability of these partial diploid strains is due to homologous genetic recombindation between the two identical copies of the phage DNA comprising the duplication. The galactose operon and the duplication of phage DNA carried by these strains is located between the phage lambda P and Q genes.

Isolation and characterization of an Escherichia coli bacteriophage requiring cell wall galactose

A new coliphage, designated U3, has been selected for the ability to discriminate the presence of galactose in the cell wall of Escherichia coli. U3 attacks E. coli K-12 cells that are able to incorporate galactose into their cell walls, but mutants blocked in the synthesis of uridine diphosphogalactose, the precursor of cell wall galactose, are completely resistant to the phage. U3 is a small, tail-less, approximately spherical phage resembling phiX174 in its physical properties. Its diameter by electron microscopy is 21 to 22 nm, and its particle weight is approximately 4 x 10(6) daltons. Like phiX174, U3 appears to have a single-stranded deoxyribonucleic acid genome and has at least four cistrons.

Polar mutations in the left arm of bacteriophage lambda i434

By studying complementation between frameshift and nonsense mutants located in the structural genes for the head of bacteriophage lambdai434, we found mutations in gene B which are polar on genes C and D and one mutation in gene E which is polar on gene F.