SEPTAL LOCALIZATION OF THE SPOIIIE CHROMOSOME PARTITIONING PROTEIN INBACILLUS-SUBTILIS

The 787 amino acid SpoIIIE protein of Bacillus subtilis is required fo r chromosome partitioning during sporulation, This process differs fro m vegetative chromosome partitioning in that it occurs after formation of the septum, apparently by transfer of the chromosome through the n ascent septum in a manner reminiscent of plasmid conjugation. Here we show that SpoIIIE is associated with the cell membrane, with its solub le C-terminal domain located inside the cell, Immunofluorescence micro scopy using affinity-purified anti-SpoIIIE antibodies shows that SpoII IE is targeted near the centre of the asymmetric septum, in support of a direct role for SpoIIIE in transport of DNA through the septum. We also report on the isolation of a mutation affecting the N-terminal hy drophobic domain of SpoIIIE that interferes with targeting to the sept um and blocks DNA transfer, This mutation also causes de-localization of the activity of the normally prespore-specific sigma factor, sigma( F), consistent with the notion that SpoIIIE can form a seal between th e chromosomal DNA and the leading edge of the division septum.