DNA polymerase III along with at least 7 other proteins binds to the origin of DNA replication in Bacillus subtilis before initiation of DNA synthesis. 4 of these genes are located near the origin. These gene products and the Po1-3 holoenzyme recognition sequence of DNA will be analyzed using purified Origin DNA. An attempt will be made to circularize this DNA so that it can replicate in an in vitro system. SPP-1 phage is known to use the host Po1-3 enzyme and appears to modify the enzyme after infection. Only one of the phage dna genes is involved. The nature of this modification and the phage DNA recognition sequence of modified Po1-3 will be analyzed.