101
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Trautner TA, Pawlek B, Günthert U, Canosi U, Jentsch S, Freund M. Restriction and modification in Bacillus subtilis: identification of a gene in the temperate phage SP beta coding for a BsuR specific modification methyltransferase. MOLECULAR & GENERAL GENETICS : MGG 1980; 180:361-7. [PMID: 6258025 DOI: 10.1007/bf00425849] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A gene coding for a modifying DNA-methyltransferase which methylates the central C in the BsuR recognition sequence 5'GGCC was identified in the genome of the temperature Bacillus subtilis phage SP beta. This gene is expressed only after induction of the prophage by either mitomycin C or UV. The presence of active methyltransferase in induced cells leads to modification of BsuR recognition sites in SP beta DNA as well as in heterologous DNA.
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102
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Dodson LA, Hadden CT. Capacity for postreplication repair correlated with transducibility in Rec- mutants of Bacillus subtilis. J Bacteriol 1980; 144:608-15. [PMID: 6776091 PMCID: PMC294708 DOI: 10.1128/jb.144.2.608-615.1980] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Bacillus subtilis strains deficient in transduction, transformation, or both were examined for the ability to remove pyrimidine dimers and to convert deoxyribonucleic acid newly synthesized after ultraviolet irradiation to high molecular weight. In one strain deficient in both recombination processes, short pieces of deoxyribonucleic acid synthesized after irradiation were not converted to high molecular weight. Two transformable strains deficient in transduction were also deficient in postreplication repair (i.e., joining of newly synthesized DNA fragments), whereas a nontransformable strain that was normal in transduction was proficient in postreplication repair. None of the transformable strains showed deficiencies in repair resynthesis or ligase activity. Our results suggest that some recombinational events may be common to transduction and postreplication repair but not to transformation, emphasizing the difference between these two pathways for genetic exchange.
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103
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Abstract
Selected platinum and ruthenium complexes were tested for their ability to cause Salmonella typhimurium strains TA98 and TA100 to revert to histidine independence. The results indicate that ruthenium compounds are capable of reverting both strains while cis-Cl2(NH3)2Pt primarily causes reversions in strain TA100. In addition, cis-platinum is an order of magnitude more mutagenic and toxic than are the ruthenium complexes. Selected compounds were also tested for their ability to induce the bacterial SOS system in the Bacillus subtilis Comptest. In this system, cis-platinum similarly showed greater inducing ability than did the ruthenium complexes. These results also demonstrated that the nature of the sixth ligand in the ruthenium compounds has a significant effect on the mutagenic capacity of these agents.
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104
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Bron S, Luxen E, Trautner TA. Restriction and modification in B. subtilis: the role of homology between donor and recipient DNA in transformation and transfection. MOLECULAR & GENERAL GENETICS : MGG 1980; 179:111-7. [PMID: 6256602 DOI: 10.1007/bf00268452] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Non-modified DNAs from phages SPO2 and phi 105, and prophage DNAs extracted from lysogens carrying these phages, were used to transfect isogenic r+m+ B. subtilis recipients which were either non-lysogenic, or had been lysogenized with a homologous or a non-homologous phage. Restriction of transfecting phage and prophage DNA occurred in non-lysogenic recipients and in recipients lysogenic for a non-homologous phage. No effect of restriction was observed when phage or prophage DNA was used to transfect recipients carrying a homologous prophage. This is analogous to the absence of restriction in transformation and indicates that in B. subtilis the distinction between transforming and transforming and transfecting DNA is not made at the initial stages of DNA uptake and processing, but rather at later stages, where recognition of homologous regions in donor and recipient DNA plays an important role.
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105
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Rubin EM, Wilson GA, Young FE. Expression of thymidylate synthetase activity in Bacillus subtilis upon integration of a cloned gene from Escherichia coli. Gene 1980; 10:227-35. [PMID: 6254841 DOI: 10.1016/0378-1119(80)90052-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The gene from Escherichia coli encoding thymidylate synthetase was cloned in the plasmid pBR322. The resulting chimeric plasmid, pER2, was effective in transforming both E. coli and Bacillus subtilis to thymine prototrophy. Uncloned linear E. coli chromosomal DNA was unable to transform thymine-requiring strains of B. subtilis to thymine independence. Linearization of the chimeric plasmid, pER2, with restriction enzymes markedly diminished its ability to transform B. subtilis auxotrophs. The Thy+ transformants derived from the transformation of B. subtilis with pER2 DNA did not contain detectable extrachromosomal DNA as demonstrated by Southern hybridization patterns and centrifugation in CsCl gradients of DNA isolated from B. subtilis colonies transformed with the chimeric plasmid. We conclude that the DNA from the chimeric plasmid was integrated into the chromosome of B. subtilis, demonstrating that extensive homology is not required for the integration of foreign DNA. This is the first reported case of a gene from a Gram-negative bacterium functioning in a Gram-positive organism.
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106
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Yasbin RE, Miehl R. Deoxyribonucleic Acid Repair in
Bacillus subtilis
: Development of Competent Cells into a Tester for Carcinogens. Appl Environ Microbiol 1980; 39:854-8. [PMID: 16345548 PMCID: PMC291433 DOI: 10.1128/aem.39.4.854-858.1980] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The development of competent transformed
Bacillus subtilis
into a tester system for carcinogens is described. Precocious or noninduced activation of SOS functions occur in competent cells. Thus, lower doses or concentrations of SOS inducing agents are needed to cause cell death due to indigenous prophage activation and lysis of bacteria. The two known defective prophages in
B. subtilis
enhance the sensitivity of competent cells to the carcinogens ultraviolet light, mitomycin C, and methyl methanesulfonate. However, these same cells have no enhanced sensitivity for the non-carcinogenic ethyl methanesulfonate or for nalidixic acid. Therefore, competent
B. subtilis
appear to be a sensitive tester for carcinogens.
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Affiliation(s)
- R E Yasbin
- Department of Microbiology and Cell Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
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107
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Abstract
Streptococcus pneumoniae R6X was lysogenized with bacteriophage 304 isolated after mitomycin induction of an ungrouped alpha-hemolytic streptococcus. Lysogenized pneumococci lost their capacity to undergo genetic transformation: transformability was restored after cells were spontaneously cured of their prophage. Both lysogens and nonlysogens produced activator substance (competence factor), and both bound deoxyribonucleic acid in a deoxyribonuclease-resistant form. However, nonlysogens retained deoxyribonucleic acid after washing, whereas lysogens did not. The latter did not liberate phage nor (unlike nonlysogens) degrade transforming deoxyribonucleic acid and contained normal levels of endonuclease.
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108
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Bresler SE, Kalinin VL, Kreneva RA. W-mutagenesis in competent cells of Bacillus subtilis. MOLECULAR & GENERAL GENETICS : MGG 1980; 177:691-8. [PMID: 6770228 DOI: 10.1007/bf00272681] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The relative yield (Nm/N) of fluorescent mutants Ind- after the transformation of Bacillus subtilis cells by means of UV-irradiated DNA is much higher in an uvr- recipient than in an uvr+ strain, when compared at equal fluence, but practically identical at equal survival. Ind- mutations are induced by UV-irradiation of separated single strands of transforming DNA. The H-strand is much more sensitive to the mutagenic action of UV light. Preliminary irradiation of competent recipient cells by moderate UV fluences increases the survival of UV- or gamma-irradiated transforming DNA (W-reactivation) and the frequency of Ind- mutations (W-mutagenesis). During transfection of B. subtilis cells by UV-irradiated prophage DNA isolated from lysogenic cells B. subtilis (phi 105 c+) c-mutants of the phage are obtained in high yield only in conditions of W-mutagenesis, i.e. in UV-irradiated recipient cells. These data show that there is no substantial spontaneous induction of error-prone SOS-repair system in the competent cells of B. subtilis.
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109
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Yoneda Y, Graham S, Young FE. Cloning of a foreign gene coding for alpha-amylase in Bacillus subtilis. Biochem Biophys Res Commun 1979; 91:1556-64. [PMID: 118759 DOI: 10.1016/0006-291x(79)91242-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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110
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Ganesan AT. Genetic recombination during transformation in Bacillus subtilis: appearance of a deoxyribonucleic acid methylase. J Bacteriol 1979; 139:270-9. [PMID: 110783 PMCID: PMC216855 DOI: 10.1128/jb.139.1.270-279.1979] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
In Bacillus subtilis the ability to take up deoxyribonucleic acid (DNA) and undergo genetic transformation may coincide with the induction of defective phage(s) and the expression of possibly related cryptic genes. A restriction-modification enzyme system appears to be expressed. Targets of the restriction activity on the DNA can be blocked my methylation catalyzed by the methyl transferase. It is shown that cellular DNA becomes progressively methylated and reaches the maxium level during the peak of competency. Deoxycytidine residues of both incoming donor and resident DNA are methylated. The possible participation of these enzymes in recombination and the general role of cryptic genes in inducible functions are discussed.
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111
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Yasbin RE, Fernwalt JD, Fields PI. DNA repair in Bacillus subtilis: excision repair capacity of competent cells. J Bacteriol 1979; 137:391-6. [PMID: 104969 PMCID: PMC218462 DOI: 10.1128/jb.137.1.391-396.1979] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Competent Bacillus subtilis were investigated for their ability to support the repair of UV-irradiated bacteriophage and bacteriophage DNA. UV-irradiated bacteriophage DNA cannot be repaired to the same level as UV-irradiated bacteriophage, suggesting a deficiency in the ability of competent cells to repair UV damage. However, competent cells were as repair proficient as noncompetent cells in their ability to repair irradiated bacteriophage in marker rescue experiments. The increased sensitivity of irradiated DNA is shown to be due to the inability of excision repair to function on transfecting DNA in competent bacteria. Furthermore, competent cells show no evidence of possessing an inducible BsuR restriction system to complement their inducible BsuR modification enzyme.
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112
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113
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Duncan CH, Wilson GA, Young FE. Mechanism of integrating foreign DNA during transformation of Bacillus subtilis. Proc Natl Acad Sci U S A 1978; 75:3664-8. [PMID: 99740 PMCID: PMC392846 DOI: 10.1073/pnas.75.8.3664] [Citation(s) in RCA: 77] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Genes encoding thymidylate synthetase from Bacillus subtilis bacteriophages were cloned in Escherichia coli. Chimeric plasmids pCD1 and pCD3 were constructed from site-specific endonuclease digests of bacteriophage phi3T DNA cloned in pMB9 in E. coli. Similar cloning techniques with bacteriophage beta22 DNA yielded chimeric plasmids pCD4, pCD5, and pCD6. Endonuclease digests of DNA from pCD1 and pCD3 propagated in E. coli or from DNA isolated from bacteriophage phi3T propagated in B. subtilis transformed B. subtilis from Thy- to Thy+. Intact DNA from bacteriophage beta22, endonuclease digests of beta22 DNA, and a chimeric plasmid (pCD5) composed only of the thybeta22 gene and pMB9 did not transform B. subtilis from Thy- to Thy+ even though pCD5 could transform Thy- E. coli to Thy+. However, if the thybeta22 fragment from pCD5 was introduced into another chimeric plasmid, pCD2, that contains a region of homology to the chromosome of B. subtilis in addition to pMB9, transformation of Thy- clones of B. subtilis was possible. Furthermore, Southern hybridization analyses of the digests of chromosomal DNA from the Thy+ transformants established that the entire chimeric plasmid was incorporated into the chromosome of B. subtilis. Treatment of these plasmids with site-specific endonucleases abolished transformation. These results indicated that the entire chimeric plasmid can be incorporated into the chromosome of B. subtilis by a Campbell-like model. Therefore, an additional mechanism for transformation exists whereby plasmids can be integrated if sufficient chromosomal homology is maintained.
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114
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Duncan CH, Wilson GA, Young FE. Biochemical and genetic properties of site-specific restriction endonucleases in Bacillus globigii. J Bacteriol 1978; 134:338-44. [PMID: 649568 PMCID: PMC222251 DOI: 10.1128/jb.134.1.338-344.1978] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Bacillus globigii contains two site-specific endonucleases, BPGLI AND BglI. A rapid technique for selection of mutants deficient in each of these enzymes was developed using sensitivity to infection by bacteriophage SP50 as an indication of the levels of enzyme. Mutants defective in BglI, BglII, and both BglI and BglII retained the wild-type modification phenotype. Genetic and biochemical studies have established that these enzymes are involved in restriction in vivo. Simplified purification procedures for BglI and BglII using these mutants are described.
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115
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116
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Abstract
Genetic transformation in recA1 strains of Bacillus subtilis was studied to test the hypothesis that, in these strains, a major pathway of recombination is missing, leaving only residual transformation via a pathway specific for transduction. The two putative recombinational pathways have been hypothesized to differ in either length of synapsed regions or specificity for nucleotide sequence homology. It was found that the efficiency of transformation of recA1 cells by deoxyribonucleic acid (DNA) from the heterologous strain W23 was much lower than when a homologous donor DNA was used, the relative efficiency being different for different genetic markers. Because the frequency of recombination between linked markers is only slightly changed in recA1 recipients, and because markers of heterologous origin in DNA from intergenotic strains are not discriminated against strongly by recA1 recipients, it is concluded that neither a difference in length of synapsed DNA nor a difference in specificity for nucleotide sequence homology accounts for reduced transformation in recA1 cells. It is proposed that at some time between uptake and integration, heterologous DNA is inactivated by restriction, and that aberrant restriction of repaired regions may account for reduced transformation by homologous DNA.
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117
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Eitner G. The influence of prophage lambda on the mutagenic response of Escherichia coli to ultraviolet irradiation. Mutat Res 1977; 44:299-304. [PMID: 333278 DOI: 10.1016/0027-5107(77)90089-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
E. coli K-12 and its lambda-lysogenic derivative were used to study the influence of lysogenic induction on the induction of mutants (streptomycin sensitivity to streptomycin resistance) by UV irradiation. The lambda-lysogenic strain responded to UV irradiation with increased sensitivity and with a strong reduction of the absolute mutant quantity, recovered per UV dose, as compared with the non-lysogenic parental strain. However, similar mutant freqqencies per surviving bacterium exclude the possibility that the diminished mutant recovery results from a selective killing of mutant cells by simultaneous induction of the processes of mutation and lysis.
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118
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Yasbin RE. DNA repair in Bacillus subtilis. II. Activation of the inducible system in competent bacteria. MOLECULAR & GENERAL GENETICS : MGG 1977; 153:219-25. [PMID: 407446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Competent B. subtilis are more UV sensitive than the non-competent population of the culture. This increased sensitivity is lose in mutants unable to induce the 'SOS system' (recA1,, recG13), in mutants defective in the induction of prophage PBSX (xin), and in late stage competent cells. Moreover, bacteriophage phi 105 produced from transfected cells are less restricted on strain YB880 than bacteriophage produced from infected cells. Therefore, competent cells (those capable of being transfected) have a DNA modification system, whereas the average log phase cell does not. These data support the hypothesis that the development of competence is correlated with the activation of derepression of the "SOS" system in B. subtilis.
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119
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Venezia RA, Matusiak PM, Robertson RG. Bactericidal factor produced by Haemophilus influenzae b: partial purification of the factor and transfer of its genetic determinant. Antimicrob Agents Chemother 1977; 11:735-42. [PMID: 301008 PMCID: PMC352059 DOI: 10.1128/aac.11.4.735] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
When aerobically grown on complex media, Haemophilus influenzae b and unencapsulated variants, Rb strains, produced a bactericidal factor that was active against other Haemophilus species and certain genera of the Enterobacteriaceae. A total of 341 clinical isolates of Haemophilus were tested for susceptibility to the factor. Ninety-three percent of H. influenzae (nontypable), 75% of H. haemolyticus, 71% of H. parainfluenzae, and 22% of H. parahaemolyticus were susceptible. H. influenaze b strains were resistant producers of the bactericidal factor and H. influenzae f strains were susceptible nonproducers. Only one strain each of H. aegyptius and H. aphrophilus was isolated and each was susceptible and resistant, respectively. 143 clinical isolates of the Enterobacteriaceae were tested and of those 82% of Escherichia coli, 85% of Salmonella sp., and all Citrobacter sp., Shigella sp., and Yersinia sp. were sensitive to the bactericidal factor produced by H. influenzae b. Attempts to isolate the bactericidal activity from mechanically disrupted, solubilized, or osmotically shocked cells failed to release active bactericidal factor. However, we partially purified the bactericidal factor from the spent culture medium of aerobically grown H. influenzae b by a series of extractions. The ability to produce the bactericidal factor was transferable to nonproducer strains without also genetically transforming for type b encapsulation. The converse was also true in that type b capsules were produced by transformed H. influenzae Rd strains but no bactericidal factor was detected from these strains. Additionally, nitrosoguanidine-induced mutants of H. influenzae b lost the ability to produce bactericidal factor without loss of their type-specific capsule, demonstrating that production of the bactericidal factor was genetically separable from production of the type capsule of H. influenzae b.
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120
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Duncan CH, Wilson GA, Young FE. Transformation of Bacillus subtilis and Escherichia coli by a hybrid plasmid pCD1. Gene X 1977; 1:153-67. [PMID: 412725 DOI: 10.1016/0378-1119(77)90026-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The gene thyP3 from Bacillus subtilis bacteriophage phi 3T was cloned in the plasmid pMB9. The resulting chimeric plasmid, pCD1, is effective in transforming both Escherichia coli and Bacillus subtilis to thymine prototrophy. The activity of the thyP3 gene product, thymidylate synthetase, was assayed and found to be 9 times greater in a transformed strain of Escherichia coli than in a phi 3T lysogen of Bacillus subtilis. The physical location of restriction sites has been determined for two related plasmids pCD1 and pCD2. Hybridization studies clearly indicate that the plasmid gene responsible for Thy+ transformation is the gene from the bacteriophage phi 3T. The lack of restriction in this transformation process is consistent with our previous studies using bacterial DNA in heterospecific exchanges indicating that the nucleotide sequence surrounding the gene is the dominant factor in determining interspecific transformation.
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121
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Piekarowicz A, Siwińska M. Inhibition of transformation and transfection in Haemophilus influenzae Rd9 by lysogeny. J Bacteriol 1977; 129:22-9. [PMID: 299746 PMCID: PMC234889 DOI: 10.1128/jb.129.1.22-29.1977] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Haemophilus influenzae Rd9 lysogenic for temperate bacteriophage N3 was found to be virtually nontransformable and nontransfectable. This inhibition of transformation and transfection was due partly to the decreased capacity of competent lysogenic cells for irreversible binding of deoxyribonucleic acid (DNA) and partly to some events taking place after adsorption of the DNA. The unadsorbed DNA was not degraded by the competent lysogenic cells.
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122
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123
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Yasbin RE, Maino VC, Young FE. Bacteriophage resistance in Bacillus subtilis 168, W23, and interstrain transformants. J Bacteriol 1976; 125:1120-6. [PMID: 815237 PMCID: PMC236191 DOI: 10.1128/jb.125.3.1120-1126.1976] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Strains of Bacillus subtilis 168 deficient in glucosylated teichoic acid vary in their resistance to bacteriophage infection. Although glucosylated teichoic acid is important for bacteriophage attachment, the results demonstrate that alternate receptor sites exist. Non-glucosylated cell wall mutants could be assigned to specific classes (gtaA, gtaB, gtaC) by their pattern of resistance to three closely related bacteriophages (phi25, phie, SP82). In addition to glucosylation, the type of teichoic acid was also important for bacteriophage attachment. B. subtilis strains 168 and W23 have different teichoic acids in their cell walls and have varied susceptibilities to bacteriophage infection. Transfer of bacteriophage resistance from strain W23 into a derivative of strain 168 was accomplished. The resistant bacteria obtained were imparied in their ability to adsorb bacteriophage and in their capacity to be transfected by bacteriophage deoxyribonucleic acid.
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124
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125
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Yasbin RE, Wilson GA, Young FE. Effect of lysogeny on transfection and transfection enhancement in Bacillus subtilis. J Bacteriol 1975; 121:305-12. [PMID: 803953 PMCID: PMC285644 DOI: 10.1128/jb.121.1.305-312.1975] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Strains of Bacillus subtilis 168 lysogenic for bacteriophage phi105 transfer with deoxyribonucleic acid (DNA) isolated from bacteriophage SPO2 at a higher efficiency than non-lysogenic strains. This enhancement of transfection was not the result of recombination between bacteriophages SPO2 and phi105. Superinfection marker rescue increased transfection with DNA from bacteriophage phi105 occurred simultaneously with the addition of the transfecting DNA. Again, this enhancement of transfection was not the result of recombination but rather a protection of the transfecting DNA by the superinfecting bacteriophage. The ability of the superinfecting bacteriophage to protect the transfecting DNA from inactivation was maximal when the bacteria were just becoming competent. Bacteriophage phi1 cannot replicate after the transfection of competent bacteria lacking a functional DNA replication system, whereas bacteriophage phi1 was able to replicate after infection of competent bacteria grown under comparable conditions. These observations support the hypothesis that GAPase and an inducible repair system play an important role in the development of competence.
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