A Prokaryotic Condensin/Cohesin-Like Complex Can Actively Compact Chromosomes from a Single Position on the Nucleoid and Binds to DNA as a Ring-Like Structure

Abstract

We show that Bacillus subtilis SMC (structural maintenance of chromosome protein) localizes to discrete foci in a cell cycle-dependent manner. Early in the cell cycle, SMC moves from the middle of the cell toward opposite cell poles in a rapid and dynamic manner and appears to interact with different regions on the chromosomes during the cell cycle. SMC colocalizes with its interacting partners, ScpA and ScpB, and the specific localization of SMC depends on both Scp proteins, showing that all three components of the SMC complex are required for proper localization. Cytological and biochemical experiments showed that dimeric ScpB stabilized the binding of ScpA to the SMC head domains. Purified SMC showed nonspecific binding to double-stranded DNA, independent of Scp proteins or ATP, and was retained on DNA after binding to closed DNA but not to linear DNA. The SMC head domains and hinge region did not show strong DNA binding activity, suggesting that the coiled-coil regions in SMC mediate an association with DNA and that SMC binds to DNA as a ring-like structure. The overproduction of SMC resulted in global chromosome compaction, while SMC was largely retained in bipolar foci, suggesting that the SMC complex forms condensation centers that actively affect global chromosome compaction from a defined position on the nucleoid.

ACKNOWLEDGMENTS

We thank the Grossman Laboratory (Massachusetts Institute of Technology) for the hyperspac plasmid and David Rudner and members of the Losick Laboratory (Harvard University) for the kind gift of the hyperspank vector. We are grateful to Uwe Linne, Gabi Schimpff-Weihland, and Mohamed Marahiel for performance of mass spectroscopy and for the kind gift of AbrB protein; to G. Muskhelishvili for the gift of Fis protein; and to Martin Neeb and Norbert Hamp for expert help in sucrose gradient centrifugation.

This work was supported by the Deutsche Forschungsgemeinschaft (Emmy Noether Programm) and the Fonds der Chemischen Industrie.

A. Volkov and J. Mascarenhas contributed equally to this work.