Induction of protein synthesis in Escherichia coli following UV- or gamma-irradiation, mitomycin C treatment or tif Expression

Molecular organization and nucleotide sequence of the recG locus of Escherichia coli K-12

The nucleotide sequence of the Escherichia coli K-12 recG gene was determined. recG was identified as an open reading frame located between the spoT operon and the convergent gltS gene. It encodes a polypeptide of 693 amino acids which was identified as a 76-kDa protein by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after it was labeled with [35S]methionine in maxicells. The sequence determined revealed no obvious promoter. Synthesis of RecG by plasmids carrying the intact gene varied with the orientation of the insert relative to the vector promoter and with the extent of upstream spoT operon sequence included in the construction. It is concluded that recG is the fourth and last gene in the spoT operon, although a possible promoter for independent transcription of spoU and recG was identified near the end of the spoT gene. The primary sequence of RecG revealed that it is related to proteins that act as helicases and has a well-conserved motif identified with ATP binding.

Molecular and functional analysis of the ruv region of Escherichia coli K-12 reveals three genes involved in DNA repair and recombination

Recombinant plasmids carrying ruvA, ruvB, or both were constructed and used to investigate the genetic defects in a collection of UV-sensitive ruv mutants. The results revealed that efficient survival of UV-irradiated cells depends on both ruvA and ruvB, and on a third gene, ruvC, located upstream of the ruvAB operon. Southern blotting analysis was used to locate insertions in ruv and to examine putative deletion mutants. Two Tn10 insertions were located to the region encoding ruvA. Since these insertions caused a deficiency in the activities of both ruvA and ruvB, we concluded that they must exert a polar effect on ruvB. Two putative ruv deletion mutants were shown to be the result of deletion-inversion events mediated during imprecise excision of Tn10. The relevant inversion breakpoints in these mutants were located to ruvA and ruvC.

Molecular organization of sbcC, a gene that affects genetic recombination and the viability of DNA palindromes in Escherichia coli K-12

The sbcC gene product of Escherichia coli interferes with the growth of a lambda red gam phage carrying a long palindrome in its DNA. This phenotype was used to identify recombinant plasmids harbouring the wild-type gene and to isolate sbcC mutant derivatives carrying Tn1000 insertions. Analysis of these plasmids located sbcC between proC and phoR at a slightly different position from that reported before (Lloyd, R.G. and Buckman, C. 1985, J. Bacteriol. 164, 836-844). Nucleotide sequencing revealed that the gene spans a DNA segment of 3.3 kb that encodes a poorly expressed protein of 118 kDa and which lies downstream of a gene of unknown function that encodes a polypeptide of 45 kDa. The amino acid sequence of SbcC contains a nucleotide binding fold similar to that in RecB and other recombination proteins.

The recR locus of Escherichia coli K-12: molecular cloning, DNA sequencing and identification of the gene product

The recR gene of Escherichia coli, which is associated with recBC-independent mechanisms of recombination and DNA repair, has been located between dnaZX and htpG on a 6.4 kb EcoRI fragment of DNA that has been cloned and analysed in lambda and plasmid vectors. Nucleotide sequencing of this interval revealed two open reading frames that constitute an operon lying immediately downstream of dnaZX. The second of these two reading frames was identified as recR. It encodes a polypeptide with a predicted molecular weight of 21,965 Daltons that migrates on SDS gels as a 26 kDa protein. The first gene of the operon encodes a polypeptide of 12,015 daltons. Its function is not known.

The recN locus of Escherichia coli K12: molecular analysis and identification of the gene product

The recN gene which is necessary for inducible DNA repair and recombination in Escherichia coli has been cloned into the low copy plasmid vector pHSG415. Analysis of the recombinant plasmid, pSP100, revealed a 5.6 Kb HindIII insert of chromosomal DNA. Transposon inactivation of recN function and analysis of a recN::Mu(Ap lac) fusion located the coding region to a 1.4 Kb region within a 2.1 Kb BglII-AvaI DNA fragment transcribed in a clockwise direction with respect to the chromosome map. The gene product was identified in maxicells as a 60,000 dalton protein. Synthesis of this protein was increased in cells lacking LexA activity or in strains carrying recN cloned into the multicopy vector pBR322. Multiple copies of recN increase resistance to ionizing radiation in recN mutants but reduce the survival of a wild-type strain.

Analysis of the ruv locus of Escherichia coli K-12 and identification of the gene product

The ruv gene of Escherichia coli, which is associated with inducible mechanisms of DNA repair and recombination, has been cloned into the low-copy plasmid vector pHSG415. The recombinant plasmid pPVA101 fully complements the DNA repair-deficient phenotype of ruv mutants. Restriction endonuclease analysis of this plasmid revealed a 10.6-kilobase (kb) HindIII DNA insert which contained a 7.7-kb PstI fragment identified as being from the chromosomal ruv region. Deletion analysis and Tn1000 insertional inactivation of ruv function located the ruv coding region to a 2.2-kb section of the cloned DNA fragment. A comparison of the proteins encoded by ruv wild-type and mutant plasmids identified the gene product as a protein of molecular weight 41,000.

Protein synthesis in Escherichia coli during recovery from exposure to low levels of Cd2+

Exposure of Escherichia coli to 3 microM Cd2+ results in 84 to 95% of the cells losing their ability to form colonies on plates of nutrient agar. Transfer of the cells to Cd2+-free liquid medium results in a recovery of colony-forming ability without significant synthesis of DNA. As an early event in recovery, the cells exhibit a rapid uptake of [3H]leucine. Recovery and this incorporation are inhibited by chloramphenicol or rifampin. Sodium dodecyl sulfate-gel electrophoresis of proteins from recovering cells labeled with [3H]leucine for 1 min indicated the synthesis of at least two classes of proteins with apparent molecular weights of 55,000 to 65,000. One class bound Cd2+ and was absent in untreated cultures. The other class of proteins, which did not bind Cd2+, was synthesized at a rapid rate in recovering cells and may be a normal cellular protein.

Lysogenization of ultraviolet-irradiated Escherichia coli with lambda: dependence on the recA and recB gene products

The lysogenization of ultraviolet-irradiated Escherichia coli cells by the lambda phage was studied. Genetic analysis indicates that changes in the number of the lysogenized cell during post-UV growth is primarily due to the change in the proteolytic activity of RecA protein. Full proteolytic activity is achieved only in the presence of the functional recB gene product.

DNA degradation, UV sensitivity and SOS-mediated mutagenesis in strains of Escherichia coli deficient in single-strand DNA binding protein: effects of mutations and treatments that alter levels of Exonuclease V or recA protein

Certain strains suppress the temperature-sensitivity caused by ssb-1, which encodes a mutant ssDNA binding protein (SSB). At 42 degrees C, such strains are extremely UV-sensitive, degrade their DNA extensively after UV irradiation, and are deficient in UV mutability and UV induction of recA protein synthesis. We transduced recC22, which eliminates Exonuclease V activity, and recAo281, which causes operator-constitutive synthesis of recA protein, into such an ssb-1 strain. Both double mutants degraded their DNA extensively at 42 degrees C after UV irradiation, and both were even more UV-sensitive than the ssb-1 single mutant. We conclude that one or more nucleases other than Exonuclease V degrades DNA in the ssb recC strain, and that recA protein, even if synthesized copiously, can function efficiently in recombinational DNA repair and in control of post-UV DNA degradation only if normal SSB is also present. Pretreatment with nalidixic acid at 30 degrees C restored normal UV mutability at 42 degrees C, but did not increase UV resistance, in an ssb-1 strain. Another ssb allele, ssb-113, which blocks SOS induction at 30 degrees C, increases spontaneous mutability more than tenfold. The ssb-113 allele was transduced into the SOS-constitutive recA730 strain SC30. This double mutant expressed the same elevated spontaneous and UV-induced mutability at 30 degrees C as the ssb+ recA730 strain, and was three times more UV-resistant than its ssb-113 recA+ parent. We conclude that ssb-1 at 42 degrees C and ssb-113 at 30 degrees C block UV-induced activation of recA protease, but that neither allele interferes with subsequent steps in SOS-mediated mutagenesis.

Induction of prophage lambda in Escherichia coli recA- strain by N-methyl-N'-nitro-N-nitrosoguanidine

Induction of prophage by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) occurred in a recA- strain lysogenic for lambda phage at a level significantly higher than the spontaneous level although the frequency was much lower than that of induction in a recA+(lambda) strain. The plaque-forming ability of lambda c17 super-infecting the recA-(lambda) strain pretreated with MNNG increased with dose of MNNG as it did for super-infection of the recA+(lambda) strain, indicating that the frequency of maturation of lambda c17 increased owing to a decrease in the immunity of the lambda lysogen with dose of MNNG given to it. Further, the activity of lambda repressor in the recA-(lambda) strain decreased after treatment with MNNG as measured by the decrease of repressor-binding activity to lambda DNA although it decreased at a 3-fold slower rate than that in recA+(lambda) strain. From these results and others previously reported we conclude that inactivation of repressor leading to MNNG-initiated prophage induction takes place through two pathways, one being the recA-dependent normal process and the other a recA-independent process unique to the effect of MNNG.

Repair and plasmid R46 mediated mutation requires inducible functions in Proteus mirabilis

In Proteus mirabilis nalidixic acid or a predose of UV induce Rec protein formation, a portion of post-UV replication repair and "post-UV replication enhancement." These inducible functions are not significantly affected by the plasmid R46, which renders P. mirabilis efficiently UV-mutable. The R46-mediated UV induction of rif mutations requires additional inducible functions, as existing after nalidixic acid treatment in rec+ strains. After a nalidixic acid pretreatment UV efficient induction of rif mutations occurs without an otherwise obligatory period of post-UV incubation prior to plating on rifampicin agar. THe inducible character of this "qualification" of plasmid R46-mediated UV mutagenesis in P. mirabilis is evident from the inhibitory effects of chloramphenicol and starvation. Constitutive high-level synthesis of Rec protein in cells harboring the recombinant (multi-copy) rec+ plasmid pPM1 reduced plasmid R46-mediated UV mutagenesis, probably by preventing (inducible?) functions required by the plasmid R46 repair-mutator.

Repair of DNA double-strand breaks in Escherichia coli cells requires synthesis of proteins that can be induced by UV light

The repair of DNA double-strand breaks in Escherichia coli cells irradiated with gamma rays occurs only after new proteins are synthesized in response to damage introduced in the genome DNA. One protein whose synthesis is thus induced is the recA protein, and previous work has shown that recA- cells do not repair double-strand breaks. However, inducing recA protein by treating cells with nalidixic acid does not induce repair of double-strand breaks, so this repair requires more than the presence of the recA protein. When repair of double-strand breaks is blocked, the genome DNA is degraded by an endonuclease-like action. Evidence is presented to show that the inducible inhibition of DNA degradation after x-irradiation [Pollard, E. C. & Randall, E. P. (1973) Radiat. Res. 55, 265] is probably caused by the inducible repair of DNA double-strand breaks.

Two mutations that alter the regulatory activity of E. coli recA protein

The Escherichia coli recA gene product is both a direct participant and a central regulatory element in important processes of DNA repair, including one that is probably responsible for all radiation mutagenesis and some chemical mutagenesis. It has the direct function of catalysing pairing of single-stranded DNA to a homologous region in duplex DNA, a reaction thought to be fundamental to genetic recombination. This activity of recA protein probably contributes to DNA repair by promoting recombination between damaged DNA molecules. We have shown that recA protein also has a regulatory function, mediated by its ability to destroy repressors and possibly other proteins by proteolytic cleavage, leading to the induction of certain genes; these include recA itself, regulated by the lexA gene product, other genes probably involved in DNA repair, some of which are also regulated by the lexA gene product, and the early genes of temperate bacteriophages, which are regulated by their repressors, recA protein is activated to cleave repressors in vitro by interaction with ATP (or the ATP analogue ATP-gamma S) and a polynucleotide such as single-stranded DNA, probably the same interaction that initiates the strand-pairing reaction. We have proposed that recA protein is also activated to attack repressors in vivo when it interacts with single-stranded DNA; DNA-damaging treatments such as UV-ray irradiation would thereby invoke the recA-dependent functions of recombination, repair, mutagenesis and prophage induction. As further evidence that the proteolytic activity of recA protein is responsible for its regulatory function, we show here that the ability of two mutationally altered recA proteins to cleave phage lambda repressor correlates with the ability of the mutant cells to induce prophage.

Induction of prophage lambda does not require full induction of RecA protein synthesis

In mitomycin C-treated lambda lysogens, even though the rate of synthesis of RecA protein was greatly reduced by a low concentration of rifampicin (4 microgram/ml), induction of prophage lambda occurred readily as assessed by (i) cell lysis of the lysogens, (ii) production of progeny phage, and (iii) extensive cleavage of lambda repressor. The extent and the rate of cleavage of lambda repressor were not significantly affected by the low rate of synthesis of RecA protein resulting from rifampicin action. However, the yield of phage progeny was reduced and lysis of the cells was slightly delayed. We conclude that in RecA+ bacteria, induction of prophage lambda does not require full induction of RecA protein synthesis.

Altered regulation of the recA gene in Escherichia coli strains carrying a recA-linked suppressor of lexA

A mutant strain of E. coli displaying altered regulation of the recA gene was isolated as a revertant of a lexA3 recA200 double mutant which showed improved DNA repair and recombination functions. The mutant (alc-24) was located between srl and recA200 and caused synthesis of high levels of recA protein in both lexA+ and lexA3 strains. The possibility that alc-24 defines the regulatory site for recA is discussed.

Dissociation of tsl-tif-induced filamentation and recA protein synthesis in Escherichia coli K-12

In Escherichia coli, expression of the tif-1 mutation (in the recA gene) induces the "SOS response" at 40 degrees C, including massive synthesis of the recA(tif) protein, cell filamentation, appearance of new repair and mutagenic activities, and prophage induction. Expression of the tsl-1 mutation (in the lexA gene) induces massive synthesis of the recA protein and cell filamentation at 42 degrees C, although other SOS functions are not induced. In this paper we show that the septation inhibition induced in tif and tsl strains at 42 degrees C is not due to the presence of a high concentration of recA protein since (i) no recA mutants (</=10(-8)) were isolated among thermoresistant nonfilamenting revertants of a tif-1 tsl-1 strain, (ii) in a tsl-1 zab-53 strain, only the low basal level of recA protein was synthesized at 42 degrees C, yet cell division was inhibited, and (iii) in a tsl-1 recA99 (amber) strain, no recA protein could be detected at 42 degrees C, yet cell division was inhibited. Among suppressors of tsl-tif-induced lethality are mutations at a locus which we call infB, located in the 66- to 83-min region. The infB1 mutation confers a highly pleiotropic phenotype, which is suggestive of a regulatory defect; it suppressed tsl-tif-induced filamentation but not recA protein synthesis, it did not suppress ultraviolet-induced filamentation (in a lon derivative), and it reduced but did not abolish tif-mediated induction of lambda prophage and bacterial mutagenesis. The dissociation of tsl-tif-induced septation inhibition and recA protein synthesis in the tif-1 tsl-1 infB1 strain suggests that the control of SOS filamentation may not be strictly identical to the control of recA protein synthesis.

Properties of Haemophilus influenzae mutants that are slightly recombination deficient and carry a mutation in the rec-1 gene region

The highly recombination-deficient rec-1 mutants of Haemophilus influenzae are, as far as tested, equivalent to recA mutants of Escherichia coli. By selection for mutations in the rec-1 gene of H. influenzae, mutants designated ird (intermediary recombination-deficient) mutants were isolated; these mutants were much less recombination deficient (degree of transformability, 0.2 to 30% of wild-type value) than previously isolated rec-1 mutants (degree of transformability, 0.0001% of wild-type value). The ird mutants were more sensitive to ultraviolet irradiation and mytomycin C treatment than the wild type, but less sensitive than rec-1 mutants. Spontaneous production of phage HP1c1 by lysogenic MC11 cells and prophage induction by mitomycin C or ultraviolet irradiation were the same as in the wild type. In the ird mutants endogenous deoxyribonucleic acid was degraded both spontaneously and after ultraviolet irradiation to the same extent as in the wild type. Examination of one of the ird mutants revealed that recombination could be enhanced by ultraviolet irradiation, possibly because of an increased synthesis of the rec-1 gene product induced by ultraviolet irradiation.

Recognition of duplex DNA containing single-stranded regions by recA protein

Genetic recombination in Escherichia coli requires recA protein, the product of the recA+ gene. In this paper we show that purified recA protein, which binds strongly to denatured DNA, cooperatively recognizes DNA containing short single-stranded regions. The interaction of varying amounts of recA protein with DNA molecules was investigated by measuring its DNA-dependent ATPase activity. In 3mM Mg2+, the ATPase activity was stimulated by excess single-stranded DNA and was minimal with either intact circular or blunt-ended linear duplexes. Single-strand gaps of about 30 nucleotides were sufficient to increase the ATPase activity to a level almost as great as that observed with single-stranded DNA. Sedimentation studies at neutral pH showed cooperative binding of recA protein to single-stranded DNA or to duplex DNA containing single-stranded regions. In the presence of ATP, an intermediate rate of sedimentation was observed; in contrast, adenosine 5'-gamma-thiotriphosphate (ATP[S]) caused the formation of fast-sedimenting DNA-protein complexes. Gapped plasmid DNA plus recA protein and ATP[S] formed large aggregates containing thousands of molecules. Complex formation and stimulation of the ATPase activity of recA protein with duplex DNA containing single-stranded regions indicates that recA protein may change the conformation of the normally duplex molecules to a conformation prepared for homologous pairing.

Four proteins synthesized in response to deoxyribonucleic acid damage in Micrococcus radiodurans

Four proteins, alpha beta, gamma, and delta, preferentially synthesized in ultraviolet light-treated cells of Micrococcus radiodurans, were characterized in terms of their molecular weights and isoelectric points. Within the sublethal-dose range, the differential rate of synthesis for these proteins increased linearly with the inducing UV dose. The degree of induction reached 100-fold, and the most abundant protein beta, amounted to approximately 2% of the total newly synthesized protein after irradiation. Damage caused by ionizing radiation or by treatment with mitomycin C also provoked the synthesis of the four proteins. The proportions between the individual proteins, however, varied strikingly with the damaging agent. In contrast to treatments which introduced damage in the cellular deoxyribonucleic acid, the mere arrest of deoxyribonucleic acid replication, caused by nalidixic acid or by starvation for thymine, failed to elicit the synthesis of either protein. Repair of deoxyribonucleic acid damage requires that a number of versatile and efficient processes by employed. It is proposed that the induced proteins participate in deoxyribonucleic acid repair in M. radiodurans. Mechanisms are discussed which would allow a differentiated cellular response to damages of sufficiently distinctive nature.

Isolation and characterization of amber mutations in the lexA gene of Escherichia coli K-12

We describe the isolation and characterization of amber mutations in the lexA gene of Escherichia coli K-12. These mutations, designated spr(Am), were isolated and characterized in a lexA tif sfi genetic background. They abolished the sensitivity of the strain to UV light and resulted in high rates of synthesis of recA protein. Phage lambda+ failed to lysogenize the strains as observed with similar strains carrying non-amber spr mutations described previously, thereby indicating a constitutive expression of the phage induction pathway. Introduction of an amber suppressor mutation into a strain bearing the spr(Am) mutation restored expression of the LexA mutant phenotype. We conclude that spr mutations either inactivate or prevent synthesis of the lexA gene product and that loss of this product results in constitutive expression of the E. coli induction system in the tif sfi genetic background.

Transient regulation of protein synthesis in Escherichia coli upon shift-up of growth temperature

Synthesis of total cellular proteins of Escherichia coli was studied upon transfer of a log-phase culture from 30 (or 37) to 42 degrees C. Cells were pulse-labeled with [3H]leucine, and the labeled proteins were analyzed by gel electrophoresis in the presence of sodium dodecyl sulfate. The rates of synthesis of at least five protein chains were found to increase markedly (5- to 10-fold) within 5 min after temperature shift-up and gradually decrease to the new steady-state levels, in contrast to the majority of proteins which gradually increase to the steady-state levels (about 1.5-fold the rate at 30 degrees C). Temperature shift-down did not cause any appreciable changes in the pattern of protein synthesis as detected by the present method. Among the proteins greatly affected by the temperature shift-up were those with apparent molecular weights fo 87,000 (87K), 76K, 73K, 64K, and 61K. Two of them (64K and 61K) were found to be precipitated with specific antiserum against proteins that had previously been shown to have an adenosine triphosphatase activity. The bearings of these findings on bacterial adaptation to variation in growth temperature are discussed.

UV-inducible repair: influence on survival, dimer excision, DNA replication and breakdown in Escherichia coli B/r Her+ cells

Using a model of double-UV-irradiation with inducing1 (non-lethal) and lethal fluences2 we have studied involvement of UV-inducible functions in post-UV-irradiation restoration processes and survival of Escherichia coli B/r thy-trp-Hcr+. Cells irratiated with both inducing and lethal fluences differed from cells irradiated with lethal fluence in the following respects: They were more UV resistant; they did not die during postincubation with chloramphenicol3; they exhibited a significant reduction in dimer excision; they were able to resume DNA replication and produce normal-sized DNA molecules in the presence of chloramphenicol. Since induction was provoked in cell prestarved for amino acids it was not associated with damage to points active in replication. However, the inducible product was more important for repair of replicating than non-replicating cells. The data indicate that protein necessary for resumption of DNA synthesis after UV is not constitutive but inducible.

The genetic characterization of lexB32, lexB33 and lexB35 mutations of Escherichia coli: location and complementation pattern for UV resistance

Mutants of LexB have been isolated by their resistance to lysogenic induction by thymine starvation, their resistance to thymine starvation and on the basis of their UV sensitivity. Here, three mutations identified originally in strains lacking mutagenic response to UV-irradiation, unmB (Kato and Shinoura, 1977), have been further characterized, mapped by P1-mediated transduction with srl into the recA-tif-zab-lexB cluster at the lexB position and analysed for complementation with various lexB and recA mutations. From the results it was concluded that unmB mutations are identical to lexB mutations; consequently these mutations have been termed lexB32, lexB33 and lexB35. The mutations lexB33 and lexB35 do not complement any of the other lexB mutations and define therefore a new complementation type. The lexB32 mutation, which like the lexB34 mutation, results in moderate UV sensitivity has a complementation pattern similar to that of lexB34. However, unlike lexB34 the lexB32 behaves like a leaky mutation. The results are discussed in relation to the recA gene product and its control.

Ribosomal abnormality in recA mutants of Escherichia coli

The tif-1 mutation has been shown to affect protein synthesis in vitro by increasing translational ambiguity (Ephrati-Elizur, Luther-Davies and Hayes, 1976). It is demonstrated here that some recA mutations confer similar abnormality. By comparing suitable combinations of ribosomes and soluble proteins from recA+ and recA cells the defect is shown to be associated with ribosomes. The recA mutation, which suppresses most phenotype characteristics of the tif-1 mutation (Castellazzi, George and Buttin, 1972(b)) does not suppress the ribosomal abnormality. Since the closely linked tif-1 and recA mutations lead to the expression of a common property they may be in the same gene.