Influence of Bacteriophage PBS1 and φW-14 Deoxyribonucleic Acids on Homologous Deoxyribonucleic Acid Uptake and Transformation in Competent Bacillus subtilis

Both bacteriophage PBS1 deoxyribonucleic acid (DNA) (in which all the thymine residues are replaced by uracil) and phage W-14 DNA in which half the thymine residues are replaced by 5-(aminobutylaminomethyl)uracil or 5-putrescinylthymine] exhibit comparable competing abilities for uptake of homologous DNA in a Bacillus subtilis competent system. But, whereas PBS1 DNA leads to a decrease in transformation frequencies compatible with its competing ability for DNA uptake, W-14 DNA decreases transformation frequencies by a factor up to eightfold higher. The effect of W-14 DNA on transformation frequencies is visible even at a concentration level that does not decrease transforming DNA uptake. No such effect was observed with heterologous DNA containing presumably ionically bound putrescine. Low concentrations of W-14 DNA decreased the number of double (nonlinked) transformants more than single transformants. The influence on transformation was abolished when W-14 DNA was added 20 min after addition of transforming DNA, i.e., when the recombination process was terminated. The putrescine-containing DNA also decreased retention of trichloroacetic acid-precipitable radioactivity of homologous DNA taken up. We conclude that W-14 DNA inhibits some intracellular process(es) at the level of recombination. In addition, there is evidence that W-14 DNA, but not heterologous DNA with ionically bound putrescine, binds also to site(s) on the cell surface other than receptors for homologous DNA.