Journal
EMBO JOURNAL
Volume 25, Issue 24, Pages 5919-5931Publisher
WILEY-BLACKWELL
DOI: 10.1038/sj.emboj.7601443
Keywords
actin; bacterial cytoskeleton; DNA segregation; sporulation
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Funding
- NIGMS NIH HHS [R01 GM073898, F32 GM065692, R01 GM 073898, GM 65692-03] Funding Source: Medline
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We here identify a protein (AlfA; actin like filament) that defines a new family of actins that are only distantly related to MreB and ParM. AlfA is required for segregation of Bacillus subtilis plasmid pBET131 (a mini pLS32-derivative) during growth and sporulation. A 3-kb DNA fragment encoding alfA and a downstream gene (alfB) is necessary and sufficient for plasmid stability. AlfA-GFP assembles dynamic cytoskeletal filaments that rapidly turn over (t(1/2) < similar to 45 s) in fluorescence recovery after photobleaching experiments. A point mutation (alfA D168A) that completely inhibits AlfA subunit exchange in vivo is strongly defective for plasmid segregation, demonstrating that dynamic polymerization of AlfA is necessary for function. During sporulation, plasmid segregation occurs before septation and independently of the DNA translocase SpoIIIE and the chromosomal Par proteins Soj and Spo0J. The absence of the RacA chromosome anchoring protein reduces the efficiency of plasmid segregation (by about two-fold), suggesting that it might contribute to anchoring the plasmid at the pole during sporulation. Our results suggest that the dynamic polymerization of AlfA mediates plasmid separation during both growth and sporulation.
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