REPLICATION THROUGH THE TERMINUS REGION OF THE BACILLUS-SUBTILIS CHROMOSOME IS NOT ESSENTIAL FOR THE FORMATION OF A DIVISION SEPTUM THAT PARTITIONS THE DNA

Germinated and outgrowing spores of a temperature-sensitive DNA initia tion mutant of Bacillus subtilis were allowed to initiate a single rou nd of replication by being shifted from 34 to 47 degrees C at the appr opriate time. The DNA replication inhibitor 6-(parahydroxyphenylazo)-u racil was added to separate portions of the culture at various times d uring the round. Samples were collected from each around the time of t he first division septation for measurements of the extent of the roun d completed, the level of division septation, the position of the sept um within the outgrown cell, and the distribution of DNA (nucleoid) in relation to the septum. The extent of replication was measured direct ly through a hybridization approach. The results show clearly that a c entral division septum can close down onto a chromosome that is only p artially replicated (to a minimum extent of about 60% of the round) su ch that DNA appears on both sides of the septum and frequently very cl ose to it. It is concluded, as claimed previously on the basis of a le ss direct approach (T. McGinness and R. G. Wake, J. Mol. Biol. 134:251 -264, 1979), that replication through the terminus region of the chrom osome is not essential for the formation of a division septum that par titions the DNA.