Cloning of a recA-like gene of Proteus mirabilis

Electroporation-mediated gene transfer efficiency is reduced by linear plasmid carrier DNAs

Carrier DNA has generally been found to stimulate DNA-mediated gene transfer of Chinese hamster ovary (CHO) cells by calcium phosphate coprecipitation. In studies employing electroporation, however, we observed that linear plasmid DNA was inhibitory to the transfection of CHO cells. This unexpected result prompted us to explore the effects of various types and forms of plasmid, cosmid, and chromosomal DNAs on transfection efficiencies. Both carrier DNA form and type were found to influence transfection efficiencies. Circular and linear forms of plasmid carrier DNA had opposite effects: circular plasmids increased and linear plasmids decreased transfection efficiencies. These effects were independent of homology with the selected plasmid and are probably independent of homologous recombination mechanisms. Bacterial genomic DNA failed to stimulate transfection, while calf thymus and cosmid DNA consisting primarily of human sequences stimulated transfection significantly. Our results have importance for plasmid-based experiments in mammalian cells such as those involving the induction of interplasmid homologous recombination.

The Escherichia coli recA gene increases resistance of the yeast Saccharomyces cerevisiae to ionizing and ultraviolet radiation

The Escherichia coli recA protein coding region was ligated into an extrachromosomally replicating yeast expression vector downstream of the yeast alcohol dehydrogenase promoter region to produce plasmid pADHrecA. Transformation of the wild-type yeast strains YNN-27 and 7799-4B, as well as the recombination-deficient rad52-1 C5-6 mutant, with this shuttle plasmid resulted in the expression of the bacterial 38 kDa RecA protein in exponential phase cells. The wild-type YNN27 and 7799-4B transformants expressing the bacterial recA gene showed increased resistance to the toxic effects of both ionizing and ultraviolet radiation. RecA moderately stimulated the UV-induced mutagenic response of 7799-4B cells. Transformation of the rad52-1 mutant with plasmid pADHrecA did not result in the complementation of sensitivity to ionizing radiation. Thus, the RecA protein endows the yeast cells with additional activities, which were shown to be error-prone and dependent on the RAD52 gene.

Expression of the Escherichia coli recA gene in the yeast Saccharomyces cerevisiae

The isolation of the protein coding region of the recA gene from Escherichia coli by extensive Bal31 digestion is described. The structural recA gene was ligated into an extrachromosomally replicating yeast expression vector, downstream of the yeast alcohol-dehydrogenase gene promoter region, to produce pADHrecA plasmid. The pADHrecA plasmid was transformed into the wild-type and the repair deficient strains of Saccharomyces cerevisiae. The crude protein samples were extracted from the individual yeast transformants. A 38 kDa protein was present in all transformants containing the recA gene on plasmid. Thus the recA gene from E coli was successfully expressed in cells from a lower eukaryote.

Cloning, sequence and expression in Escherichia coli of the Methylobacillus flagellatum recA gene

By means of interspecific complementation of an Escherichia coli recA- mutation with phasmids containing a gene bank from an obligate methylotroph, Methylobacillus flagellatum (Mf), the recA+ gene from this bacterium was identified. When expressed in an E. coli recA- host, it can function in recombination, DNA repair, and prophage induction. The nucleotide sequence of the gene has been determined. The coding region consists of 1032 bp specifying 344 amino acids. The deduced RecA protein structure shows a striking homology with RecA from other bacteria, except for the C-terminal region and some residues which were proposed to be responsible for the coprotease ability of RecA proteins. The region preceding the recA-Mf gene start codon has no SOS box--the LexA repressor binding site. Expression of the recA-Mf gene in E. coli proved to be DNA-damage independent.

Molecular analysis of the Bacteroides fragilis recA gene

The nucleotide sequence of a 2.5-kb DNA segment containing the Bacteroides fragilis recA gene was determined. The coding region of the recA gene specifies a protein of 318 amino acids. The RecA protein of B. fragilis shows significant homology with that of Escherichia coli, Thiobacillus ferrooxidans, Pseudomonas aeruginosa and Proteus mirabilis. No SOS box characteristic of LexA-regulated promoters could be identified in the 5'-noncoding region of the B. fragilis recA gene. Promoter activity of the cloned recA gene in E. coli was located within a 113-bp fragment of the B. fragilis DNA by in vitro construction of operon fusions with a promoterless lacZ gene. The transcription start point for this gene in B. fragilis was determined by primer extension analysis.

Transcriptional and translational analyses of recA mutant alleles in Pseudomonas aeruginosa

Recombinant plasmids containing the recA gene from Pseudomonas aeruginosa were used in complementation, transcriptional, and translational studies to examine the nature of rec-102 and rec-2, mutations which confer a recA-like mutant phenotype on P. aeruginosa PAO strains. For comparison, recA7::Tn501 mutants of strain PAO were constructed by gene replacement. The rec-2 and rec-102 alleles were shown to be recA alleles; plasmids containing the recA gene complemented the three rec mutant strains for defects associated with recA mutation. Northern blot analyses indicated that the recA gene in P. aeruginosa was transcribed as two distinct mRNAs of approximately 1.2 and 1.4 kilobases (kb). A plasmid encoding both transcripts of recA complemented all defects associated with the three recA mutations rec-2, rec-102, and recA7. However, a 2.4-kb subclone (pJH13) encoding only the smaller transcript of the recA gene was expressed differently in the three recA allele backgrounds and served as a tool to distinguish the nature of the rec-2 and rec-102 mutations in recA. A minicell analysis showed that a plasmid expressing both of the recA gene transcripts or one that expressed only the smaller transcript both produced the same 42-kilodalton recA protein. A chloramphenicol acetyltransferase gene fusion in the 3' end of the recA transcript showed that the recA gene of P. aeruginosa was induced following treatment with a DNA-damaging agent (methyl methanesulfonate). The recA7 mutant constructed here showed no recA-related transcript or protein under inducing conditions, and pJH13 in this host produced only low levels of the smaller recA transcript and low levels of recA protein. The rec-2 mutant produced a detectable transcript but no recA protein following induction. The presence of low levels of activated recA protein encoded by pJH13 in the rec-2 mutant resulted in wild-type transcriptional levels of chromosomally encoded recA, but no recA protein was detectable. Thus, the rec-2 allele of recA was normal with respect to induction of mRNA, but these transcripts were defective in either translation or synthesis of a stable protein. The rec-102 mutant also produced a detectable transcript and no recA protein following induction, but having pJH13 in the cell to produce low levels of activated recA protein resulted in overproduction of chromosomally encoded recA transcripts and active recA protein. Thus, the recA defect in the rec-102 mutant is apparently in the interaction between recA and a lexA-like repressor.

Molecular cloning of a recA-like gene from the cyanobacterium Anabaena variabilis

A recA-like gene isolated from the cyanobacterium Anabaena variabilis was cloned and partially characterized. When introduced into Escherichia coli recA mutants, the 7.5-kilobase-pair plasmid-borne DNA insert restored resistance to methyl methanesulfonate and UV irradiation, as well as recombination proficiency when measured by Hfr-mediated conjugation. The cyanobacterial recA gene restored spontaneous but not mitomycin C-induced prophage production. Restriction analysis and subcloning yielded a 1.5-kilobase-pair Sau3A fragment which also restored methylmethane sulfonate resistance and coded for a 38- to 40-kilodalton polypeptide when expressed in an in vitro transcription-translation system.

Inhibition of mutation induction and unchanged mutational specificity in Escherichia coli K12 overproducing the RecA protein

Induced mutagenesis was studied in Escherichia coli K12 cells in relation to the level of RecA-protein (P-RecA). In experiments strains AB2497, AB2497(pBR322) and AB2497(pX02) were used. The multicopy plasmid pX02 is a recombinant of pBR322 and recA+ gene of E. coli K12. Cells carrying this plasmid overproduce the P-RecA constitutively. Mutagenesis was induced by the decay of incorporated 6-3H-thymidine. Mutations of the argE3 (ochre) to Arg+ prototrophy were followed. Besides the frequency of mutations, mutagenic specificity was determined. In cells AB2497(pX02) which overproduce the P-RecA the yield of Arg+ revertants was markedly reduced compared with that in strains AB2497 or AB2497(pBR322), whereas the mutagenic specificity was not changed. In all the strains studied the predominant type of mutation produced was the base substitution in the A:T base pair.

Cloning and expression in Escherichia coli of a recA-like gene from Bacteroides fragilis

The recombinant plasmid pHG100, containing a 5.2-kb DNA fragment from Bacteroides fragilis, complemented defects in homologous recombination, DNA repair and prophage induction to various levels in an Escherichia coli recA mutant strain. There was no DNA homology between the cloned B. fragilis recA-like gene and E. coli chromosomal DNA. pHG100 produced two proteins with Mr of approx. 39,000 and 37,000 which cross-reacted with antibodies raised against E. coli RecA protein. The production of these proteins was not increased after UV induction. The cloned B. fragilis recA-like gene product did not enhance the production of native but defective E. coli RecA protein after UV irradiation.

Molecular cloning of a recA-like gene of Methylophilus methylotrophus and identification of its product

A recombinant plasmid, pPF5, has been constructed which contains a 5.5-kb fragment of Methylophilus methylotrophus DNA inserted into pAT153, and which confers resistance to UV and mitomycin C (MC) upon Escherichia coli recA mutants. Hybridisation analysis indicates that sequence homology exists between the cloned DNA and a fragment of E. coli chromosomal DNA that contains the recA gene. Tn1000 insertions have been isolated within pPF5 that inactivate its ability to complement recA mutations, and the site of each insertion has been determined by restriction mapping. A 36-kDa protein is synthesised by pPF5 but not by any of the Tn1000 derivatives, indicating that this protein is the product of the gene responsible for the complementation. Comparison of the size of truncated polypeptides produced by selected pPF5::Tn1000 derivatives with the position of the insertion sites of the transposon, gave the direction of transcription of the M. methylotrophus recA+ gene. SOS proteins are induced in E. coli recA mutants harbouring pPF5 following MC treatment.

Expression of the Proteus mirabilis recA gene in Bacillus subtilis is directed by its own promoter

The recA gene of Proteus mirabilis (recApm) has been cloned into the PstI site of the Bacillus promoter-probe plasmid pPL603. When present on this plasmid, the recApm1) gene is expressed in B. subtilis under the control of its own transcriptional and translational signals. It is concluded that the high AT-content of the DNA sequence upstream of the -35 region is of decisive importance for the usage of the recApm promoter by the B. subtilis RNA polymerase. The results are discussed in relation to the expression barriers found to exist for genes from gram-negative bacteria in the gram-positive B. subtilis.

The sfiA11 mutation prevents filamentation in a response to cell wall damage only in a recA+ genetic background

N-alpha-palmitoyl-L-lysyl-L-lysine dihydrochloride ethyl ester (PLL) at sublethal doses causes filamentous growth of E. coli strains except sfiA mutants, which divide normally in its presence. PLL does not elicit the SOS responses as judged by lambda prophage induction, an increase of RecA protein synthesis or induction of the sfiA operon in a sfiA::lacZ fusion strain. Thus, it appears that filamentation caused by PLL is not an SOS function and might be the result of membrane damage by PLL, which is an amphipathic compound and at higher doses causes cell lysis. This indicates that basal levels of the sfiA gene product are sufficient to inhibit cell division in the presence of PLL. We have found further that the phenotype of the sfiA mutation in the presence of PLL requires a recA+ genetic background and does not occur in E. coli recA1 sfiA11, recA13 sfiA11, recA56 sfiA11 and recA441 sfiA11. All these strains, but rec441 sfiA11, however, regain the ability of sfiA11 mutants to divide in the presence of PLL after transformation with the RecA overproducing-plasmid pXO2. This supports the conclusion that the RecA protein positively affects sfiA11-mediated cell division in the presence of the cell membrane damaging compound, PLL. The basal level of the RecA protein in the recA+ sfiA11 strain is sufficient for this process. An increased level due to overproduction from the multicopy plasmid pXO2 exerts the same effect.

Resistance to chloramphenicol in Proteus mirabilis by expression of a chromosomal gene for chloramphenicol acetyltransferase

Proteus mirabilis PM13 is a well-characterized chloramphenicol-sensitive isolate which spontaneously gives rise to resistant colonies on solid media containing chloramphenicol (50 micrograms ml-1) at a plating efficiency of 10(-4) to 10(-5). Such chloramphenicol-resistant colonies exhibit a novel phenotype with respect to chloramphenicol resistance. When a single colony grown on chloramphenicol agar is transferred to liquid medium and grown in the absence of antibiotic for 150 generations, a population of predominantly sensitive cells arises. This mutation-reversion phenomenon has been observed in other Proteus species and Providencia strains, wherein resistance has been shown to be mediated in each case by the enzyme chloramphenicol acetyltransferase. The cat gene responsible for the phenomenon is chromosomal and can be cloned from P. mirabilis PM13 with DNA prepared from cells grown in the absence or the presence of chloramphenicol. Recombinant plasmids which confer resistance to chloramphenicol carry an 8.5-kilobase PstI fragment irrespective of the source of host DNA. The location of the cat gene within the PstI fragment was determined by Southern blotting with a cat consensus oligonucleotide corresponding to the expected amino acid sequence of the active site region of chloramphenicol acetyltransferase, and the direction of transcription was deduced from homology with the type I cat variant.

Protection of nonmodified phage lambda against EcoK restriction mediated by recA protein

A study was conducted to establish whether the EcoK-specific restriction, which is alleviated in E. coli cells after UV induction of the SOS response (Day 1977), is also alleviated under the influence of an increased level of recA protein without induction of other SOS functions. The host cells used were E. coli K-12, strain AB2497, and its derivatives; the nonmodified phage lambda was a mutant b2b5(vir). An increase of the recA protein level was induced using the plasmid pX02, which is a recombinant of pBR322 carrying the recA gene of E. coli. AB2497(pX02) cells were found to exhibit a lower level of restriction than those without plasmid. The results indicate that the recA protein protects phage DNA during the process of restriction. A further factor affecting restriction is the growth phase of the culture of the restricting host: cells in the late stationary phase exhibit lower restriction than those in the exponential phase of growth. By a combination of these two factors (presence of plasmid pX02 and stationary growth phase) one can reduce the restriction of nonmodified phage about 300 times.

Functional substitution of the recE gene of Bacillus subtilis by the recA gene of Proteus mirabilis

Rec mutants of Bacillus subtilis have been tested for complementation by the recA gene of Proteus mirabilis (recApm) which was introduced into B. subtilis via the plasmid pHP334. In the recE4 mutant of B. subtilis the plasmid pHP334 restored significantly the defects in RecE functions tested: UV-sensitivity, homologous recombination (transduction and transformation) and prophage induction. Although serological methods to detect the presence of RecApm protein in B. subtilis have been unsuccessful, our results strongly indicate that the recE function of B. subtilis is analogous to the recA function of P. mirabilis.

P. mirabilis RecA protein catalyses cleavage of E. coli LexA protein and the lambda repressor in vitro

The cloned recA+ gene of proteus mirabilis substitutes for a defective RecA protein in Escherichia coli recA- mutants, and restores recombination, repair and phage induction functions to near normal levels. In a previous report, we described the purification and characterisation of the recombination activities of the P. mirabilis RecA protein (West et al. 1983b ). In this paper, we show that the purified protein catalyses the cleavage of both the Escherichia coli LexA protein and the bacteriophage lambda repressor in vitro. These results provide a direct biochemical basis for the interspecies complementation observed in vivo and suggest that P. mirabilis has an SOS regulatory network similar to that of E. coli.

Interspecies recA protein substitution in Escherichia coli and Proteus mirabilis

With the help of recombinant plasmids carrying the recA gene of Escherichia coli or of Proteus mirabilis the ability of the recA gene products to substitute functionally for each other was studied. The recA protein of each can function in recombination, repair, induction of mutations and prophages and in regulation of its own synthesis within the foreign host nearly equally well as in the natural host. It is, therefore, suggested that recA-dependent processes act similarly in E. coli and P. mirabilis.

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.