Topography of Chromosome Membrane Junction in Bacillus subtilis

Abstract

THE association between bacterial chromosomes and membranes has been well documented^1–4. In B. subtilis three unique chromosomal sites, the replication point, the replication origin and the terminus, were found selectively in association with fast sedimenting materials in cell lysates^5–7. Previously, we have reported that the B. subtilis chromosome replicates bidirectionally and that one direction was terminated shortly after initiation⁸. It is inferred that the origin and terminus are physically separated by a short segment of chromosome even when the chromosome is circular. We designate this chromosomal segment as the shorter chromosome segment in contrast to the other longer segment which is replicated in the opposite direction, as a unit, by one of the forks. Previous data on origin terminus membrane association^6,7 should therefore be interpreted as either that the chromosome attaches to the membrane at two separate sites, the origin and the terminus, or that a fairly long chromosomal segment which includes both origin, terminus and other markers on the shorter segment is associated with the membrane. These alternatives can now be tested experimentally because several mutants with different genetic markers between the origin and terminus on the chromosome segment have become available⁸.