Heat-activated endonuclease in Bacillus subtilis

Transformation-deficient mutants of Bacillus subtilis impaired in competence-specific nuclease activities

A comparison of the nucleolytic activities in competent and physiologically low-competent wild-type cultures of Bacillus subtilis in DNA-containing sodium dodecyl sulfate-polyacrylamide gels revealed the existence of three competence-associated nuclease activities with apparent molecular weights of 13,000, 15,000, and 26,000. The three activities, which were dependent on manganese or magnesium ions, were specifically present in the competent fraction of a competent culture. The competence-associated nucleolytic activities of eight transformation-defective mutant strains were assayed, resulting in the following three classes of mutants: (i) four strains which, according to this assay, were not impaired in any of the nucleolytic activities mentioned above; (ii) one strain which was strongly impaired in the 13,000- and 26,000-molecular-weight activities, but showed a considerable level of the 15,000-molecular-weight activity; and (iii) three strains which were severely impaired in all three activities. The results indicated that the 26,000-molecular-weight activity was a dimer of the 13,000-molecular-weight activity and that this nuclease was involved in the entry of DNA.

Purification and properties of a manganese-stimulated deoxyribonuclease produced during sporulation of Bacillus subtilis

A DNAase (deoxyribonuclease) was isolated from culture supernatants of sporulating Bacillus subtilis 168. The purified enzyme migrated as a single band during polyacrylamide-gel electrophoresis. The enzyme differs from other DNAases of B. subtilis in molecular weight, metal-ion requirement and mode of action. The enzyme was inactive in the absence of metal ions, and exhibited optimum activity with 10 mM-Mn2+, although Mg2+, Cd2+ and Co2+ could also permit some activity. The pH optimum for the enzyme was pH 7.5, and it degraded linear-duplex DNA or closed-circular-duplex DNA to acid-soluble material. There was little or no activity on single-stranded DNA or rRNA. Sucrose-gradient analysis of the products of DNAase action on bacteriophage T7 DNA showed that endonucleolytic cleavage had occurred by the introduction of single-strand breaks in both strands of the duplex. The molecular weight of the enzyme was determined, by gel filtration on Sephadex G-75, to be 12000.

Properties of the high-molecular-weight deoxyribonuclease of Bacillus subtilis degrading single-stranded DNA

We have studied the properties of the high-Mr DNAse degrading single-stranded DNA which is present in extracts of Bacillus subtilis. This enzyme is a heterogeneous aggregate of identical subunits with an Mr of 36 000, as measured in dodecylsulfate/polyacrylamide electrophoresis. The aggregate can be disassembled by the presence of Triton X-100, but reforms spontaneously following removal of the detergent. A mild proteolytic treatment of the aggregate causes the irreversible and nearly quantitative conversion into the free subunit. The modified subunit has identical properties (in terms of size, chromatographic adsorption and catalytic activity) as the small DNAse previously described by Ciarrocchi et al. [Eur. J. Biochem. 61, 487 (1976)], i.e. an endonuclease highly specific for single-stranded DNA and producing 5'-P and 3'-OH ends.

An intracellular endonuclease of Bacillus subtilis specific for single-stranded DNA

We have fractionated from extracts of Bacillus subtilis the DNase activity specific for single-stranded DNA; the activity separates in two main fractions on Sephadex G-200, a larger one (Mr greater than 400 000) and a smaller one (Mr approximately 30 000). We have purified the smaller, more abundant fraction nearly 3000-fold. The purified enzyme has a pH optimum close to 8, is activated by Ca2+, and is inhibited by EDTA; the enzyme hydrolyses single-stranded DNA at a rate approximately 40 times greater than double-stranded DNA. The mode of action is endonucleolytic on both substrates, but the possiblility that the two activities may reside on different molecules is not ruled out. The products have 5'-P and 3'-OH ends. The enzyme is different from those purified from the culture media of the same organism in several respects; the latter are all extracellular enzymes, they are not specific for single-stranded DNA (except one) and have all an exonucleolytic mode of action.

Interactions between exogenous deoxyribonucleic acid and membrane vesicles isolated from Bacillus subtilis 168

Membrane vesicles isolated from competent cultures of Bacillus subtilis 168 bound up to 20 mug of double-stranded deoxyribonucleic acid (DNA) per mg of membrane protein in the presence of ethylenediaminetetraacetate. The formation of the DNA-membrane complex was time, temperature, and pH dependent. Eighty per cent of the DNA could be removed from the complex by treatment with deoxyribonuclease I. Nevertheless, the DNA that remained attached to the vesicles appeared to have been attacked by the enzyme, suggesting that all the complexed DNA is located at the outer surface of the vesicles. Pretreatment of DNA with deoxyribonuclease I destroyed its affinity for the vesicles. The extent of binding decreased by the addition of Mg(2+) ions, especially at high DNA concentrations (more than 2 mug/ml). This effect was partially due to membrane-associated Mg(2+)-dependent endonucleolytic activity, which caused double-strand breaks in addition to single-strand nicks, and to exonuclease activity. The endonucleolytic activity was enhanced by heating the membranes at 80 C. DNA-membrane association was not markedly affected by sulfhydryl reagents, but was largely inhibited by formaldehyde. Endogenous competence-stimulating activity did not alter the DNA-binding capacity of the vesicles.

In vitro repair of x-irradiated DNA extracted from Bacillus subtilis deficient in polymerase I

DNA extracted from x-irradiated cells of a mutant of Bacillus subtilis deficient in DNA polymerase I has greatly reduced biological activity. This DNA, which has many single-strand nicks, can be repaired in vitro with purified DNA polymerase I and DNA ligase or with lysates of wild-type B. subtilis cells, which restore biological activity and increase the single-strand molecular weight. Lysates of polymerase I-deficient B. subtilis cells cannot repair such irradiated DNA until purified DNA polymerase I or lysate from wild-type cells is added to the deficient lysate.

Bacterial inactivation of transforming deoxyribonucleate

Competent and noncompetent bacteria are able to bind deoxyribonucleate (DNA). The consequence of this binding is different for the two types of bacteria. Competent bacteria are able to utilize the DNA for transformation. DNA exposed to noncompetent bacteria loses its biological activity with a coincident reduction in the double-stranded molecular weight. The reduction in molecular weight does not appear to be sufficient to account for the loss of biological activity observed.

Effects of pH on transformation of Bacillus subtilis with single-stranded deoxyribonucleic acid

Variation in frequencies of transformation mediated by native and single-stranded DNA and its dependence on pH of the medium were investigated. The results indicate that the biological activity of deoxyribonucleic acid (DNA) of both configurations assayed in the presence of ethylenediaminetetraacetic acid (EDTA) increases as the pH of the transformation mixture is lowered from 7.7 to a maximum transformation frequency near pH 6.1. At this lower pH, native DNA transforms equally in medium with and without EDTA, and single-stranded DNA is 0.4 to 0.6 as active as native DNA in transforming Bacillus subtilis. A high efficiency of transformation with single-stranded DNA was observed for five markers in three recipient strains. The increased efficiency of native DNA appears to be caused by a lesser capacity of EDTA to bind magnesium at the lower pH. The increased efficiency of single-stranded DNA at pH below 7.0 results from decreased activity of a single-strand specific nuclease present in competent populations.

Abortive infection of sporulating Bacillus subtilis 168 by phi 2 bacteriophage

Bacteriophage phi2 is unable to replicate in Bacillus subtilis 168. Although some phage deoxyribonucleic acid (DNA) synthesis can occur, the DNA made is not biologically active and sedimentation analysis reveals that it is smaller in size than that of mature DNA or DNA isolated from phi2-infected permissive hosts. Messenger ribonucleic acid hybridizable with phi2 DNA is also synthesized in phi2-infected cells of 168. Mutants of 168 which are permissive hosts for phi2 have been isolated. These mutants are defective in sporulation and possess the phenotype of "early sporulation mutants." The majority map in two locations, one near the lys locus opposite the trp locus (spoA locus) and the other tightly linked to a phe locus.