Deoxyribonucleic acid-membrane complexes in the Bacillus subtilis transformation system

Heterospecific transformation in Bacillus subtilis: protein composition of a membrane-DNA complex containing unstable heterologous donor-recipient complex

Previously it was demonstrated that, in contrast to the homologous donor-recipient complex, the unstable heterologous donor-recipient complex remains bound to the cellular membrane. To examine whether proteins known to be involved in the processing of transforming DNA in Bacillus subtilis are associated with membrane fragments which carry chromosomal DNA, a crude membrane-DNA complex was subjected to electrophoresis through a sucrose gradient. This resulted in the separation of membrane fragments associated with DNA and free membrane fragments. By means of two-dimensional gel electrophoresis several proteins, either uniquely present or considerably enriched in the purified membrane-DNA complex, were detected. Among these proteins we identified the 45 kD recE gene product, required for recombination, the 18 kD binding protein involved in the binding of transforming DNA and a 17 kD nuclease involved in the entry of transforming DNA. These results suggest that the membrane sites at which donor DNA integrates into the recipient chromosome are in the vicinity of the sites of entry of donor DNA through the membrane.

Molecular fate of heterologous bacterial DNA in competent Bacillus subtilis: further characterization of unstable association between donor and recipient DNA and the involvement of the cellular membrane

Although heterospecific transformation is extremely inefficient and very little heterologous donor DNA integrates into the recipient chromosome in a stable way, we have previously shown that B. pumilus DNA entering competent B. subtilis efficiently associates with the recipient chromosome in an unstable way. This association can be stabilized by photocrosslinking in the presence of 4,5',8-trimethylpsoralen; it depends on the recombination proficiency of the recipient strain and on strand-separation of the recipient chromosome (te Riele and Venema 1982b). The present study provides further evidence that the heterologous donor DNA and the recipient DNA are associated by regions of base-pairing. Based on the high sensitivity of the donor moiety in the complex to nuclease S1 (90%) and the high sensitivity of the complex to moderate denaturing conditions (Tm = 48 degrees C), we presume that donor and recipient DNA are associated either by several short sequences of 15-25 fairly well matched base pairs or by a region of base-pairing of about 200 bases, which contains 25% of mismatches. During incubation, the unstable complex disappears, probably due to nucleolytic degradation. The unstable heterologous donor-recipient complex (DRC) was found to be membrane-bound. However, in contrast to homologous DRC, the unstable heterologous DRC remains membrane bound during incubation. Apparently, the predominantly single-stranded character of the heterologous DRC prevents release of the complex from the membrane.

Heterologous deoxyribonucleic acid uptake and complexing with cellular constituents in competent Bacillus subtilis

With competent cultures of Bacillus subtilis the uptake of Escherichia coli deoxyribonucleic acid (DNA) is about 50% that for homologous DNA. Uptake of phage T6 DNA, if any, is of the order of 7%, while nonglucosylated phage T6 (T6) DNA is taken up almost as effectively as homologous DNA. Both T6 and T4 DNA interfere only minimally with uptake of homologous DNA; by contrast, T6 DNA competes with homologous DNA as effectively as the latter itself. These results indicate that the glucose residues in the T-even phage DNA, located in the large groove of the DNA helix, reduce affinity for cellular receptors, leading to low binding of T6 DNA. The latter DNA is considerably less degraded by extracellular nucleases than homologous DNA, thus excluding enzymatic hydrolysis as the source of poor uptake. Affinity of DNA for competent cells was also evaluated by the formation, and detection in a CsCl density gradient, of complexes of DNA with cellular constituent(s). Such comlexes, similar to those previously observed with transforming DNA, are formed by E. coli DNA and T6 DNA; in reconstruction experiments the denatured forms of these same DNA samples form complexes when added to the cells before lysis. T6 DNA, on the other hand, does not form such a complex. The possible role of such complexes in transport of DNA to the cell interior is discussed.

Transformation of Bacillus subtilis: transforming ability of deoxyribonucleic acid in lysates of L-forms or protoplasts

The transformation of Bacillus subtilis by homologous deoxyribonucleic acid (DNA) made available by gently lysing a stable L-form or protoplast suspension was 3 to 10-fold more efficient than DNA isolated by conventional procedures. This increased transformation was not influenced by digestion with pronase, trypsin, or ribonuclease. Preincubation of isolated DNA with L-form lysates did not increase the transformation efficiency above that achieved with untreated, isolated DNA. In addition to displaying a higher efficiency of transformation, the DNA found in these gently prepared lysates was also able to co-transform heretofore unlinked markers at frequencies in excess of those found by congression. Comparison of the frequency of multiple marker transformations to single marker events as a function of DNA dilution conclusively proves that these markers originated from the same continuous strand of DNA.

In situ activity of enzymes on polyacrylamide gels of a deoxyribonucleic acid-membrane fraction extracted from pneumococci

A deoxyribonucleic acid (DNA)-membrane fraction extracted from Diplococcus pneumoniae was subjected to polyacrylamide gel electrophoresis after treatment with 0.16% sodium dodecyl sulfate. At least two DNA polymerase activities were detected by in situ assays with appropriate substrates, templates, and inhibitors, including a co-polymer of deoxyadenylic and thymidylic acid and N-ethylmaleimide. This activity coincided with a fraction in the gel containing 7.5, 9.4, and 24%, respectively of the DNA, phospholipid, and protein present in the DNA-membrane fraction before electrophoresis and sodium dodecyl sulfate treatment. Assays with minced gels showed that several nuclease activities, deoxyribonucleotide kinase activity, and DNA ligase activity also coincided with this fraction. However, ribonucleoside diphosphate reductase activity did not. These results demonstrate that a complex of enzymes involved in DNA replication is firmly bound to the DNA-membrane fraction in pneumococci.