Interaction between deoxyribonucliec acid and distamycin A studied by transformation in Bacillus subtilis

Aspects of specific DNA-protein interaction; local bending of DNA molecules by in-register binding of the oligopeptide antibiotic distamycin

Distamycin A binds strongly/moderately to DNA below/above r = 0.08 molecules bound per DNA phosphate. Titration viscometric measurements for high and low molecular weight DNA yielded the relative changes of DNA persistence length, delta alpha/alpha 0, and contour length, delta L/L0 (Nucl. Acids Res. 7 (1979) 1375). delta L/L0 is negligible/positive in the range below/above r = 0.09 at 0.2 M Na+! A two-line covering of the small groove by ligand molecules explains the increase of contour length. The characteristic delta alpha/alpha 0 drop is quantitatively interpreted by local DNA bending (kinking). The underlying theoretical basis is presented in two appendices and applied, in a third one, to literature data for the DNA-actinomycin system. The angle gamma of local DNA bending as induced by complex formation with different distamycin derivatives is presented for DNA species of different base composition. By means of appropriate model, a length mismatch per dinucleotide of (0.03(2) +/- 0.01)nm [or (0.04(3) +/- 0.01)nm] was derived from the experimentally obtained bending angle per dinucleotide of (1.6 +/- 0.4)0 [or (2.1 +/- 0.05)0], independent of DNA base composition and distamycin chain length.

A novel endonuclease of human cells specific for single-stranded DNA

We have fractionated from human aneuploid cell cultures three different enzyme fractions degrading single-stranded DNA. We have purified and characterized one of these DNases; this is an endonuclease working at alkaline pH (around 9.5) and requiring Mg2+ for its activity. The enzyme degrades denatured DNA over 100 times more efficiently than native DNA in optimal conditions. The termini produced by the enzyme have 5'P and 3'OH ends. The enzyme can attack, though at reduced rate, the supertwisted circular molecule of Simian virus 40 DNA, whereas it is inactive on the nicked circular molecule. The ultraviolet irradiation of DNA, whether native or denatured, does not affect its efficiency as substrate of the DNase. The properties of this endonuclease distinguish it from those of the other DNases described previously in mammalian cells; the denomination DNase VI is therefore proposed. Its properties are similar to those of DNases described in Ustilago maydis and Bacillus subtilis, for which an essential role in recombination seems likely.

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.

Genetic and physiological studies on the site of action of distamycin A

Two new genetic loci of Bacillus subtilis are identified by mutations that confer resistance to distamycin A and to other antibacterial agents. The chromosomal region where they map probably contains a cluster of genes whose products are related to membrane structure and function. Some of the biological effects of distamycin A are still in evidence in the resistant mutants indicating that the drug possibly acts at multiple sites. Most biological effects of the drug (including the phenotypic correction of a morphopoietic mutation) are likely to be due to the interaction of distamycin A with membrane (or surface) structures.

Evidence for two waves of induction of DNA enzymes in stimulated human lymphocytes

The stimulation of human lymphocytes with phytohaemoagglutinin induces the appearance or increase of several enzymes of DNA metabolism [Pedrini etal., Biochem. Biophys. Res. Comm., 47:1221(1972)]. With long times of stimulation, two phenomena are observed; an increase in the levels of DNA polymerase, of a DNase acting on single-stranded DNA, and of an endonuclease, occurring between the third and fourth day, in parallel with a wave of DNA synthesis;a second wave of increase of the same enzymes and of DNA ligase,occurring between the fifth and eight day when the DNA replication rate, as measured by thymidine-pulses, has decreased to values close to the background.

Properties of a Bacillus subtilis strain lacking DNA polymerase I

We have isolated a mutant of Bacillussubtilis deficient in DNA polymerase I, denominated polA42, which shows a reduced ability to repair the damage to DNA by UV radiation, MMS and mitomycin C;the ability to perform recombination is not appreciably impaired.DEAE cellulose chromatography allows the separation of polymerases I and II from the parental strain;a simple procedure is also described which allows to separate rapidly the polymerases II and III of the mutant strain. The three separated polymerases have similar catalytic properties but they can be distinguished for their sensitivity to inhibitors: PCMB inhibits polymerases II and III but not polymerase I; HPUra inhibits only polymerase III. All three enzymes are unaffected by nalidixate. The DNA synthesis occurring in cells of the polA42 strain permeabilized with toluene is inhibited by nalidixate, whereas the synthesis occurring in polA(+) toluenized cells is unaffected by the drug. The polA gene has been mapped by transduction and localized between the phe(12) and argA(3) genes.