A four-stranded DNA from Bacillus subtilis which may be an intermediate in genetic recombination

DNA of Bacillus subtilis strain UVSS 19--8M, of high ultraviolet sensitivity, was isolated after cultivating in medium containing bromouracil. Isopycnic banding in CsC1 shows an unusual pattern with four bands, including an extra one halfway between those for hybrid and for DNA of this band, amounting to 15--25% of the total DNA mass in one preparation, was isolated and investigated. The characteristics found for this DNA are in agreement with a four-stranded DNA unit similar to one of the structures postulated by Holliday as intermediates during genetic recombination. UVSS 19--8M from which this DNA has been isolated is shown to be defective for transformation and transfection, and can be regarded as rec-.