SMC complexes sweeping through the chromosome: going with the flow and against the tide

Bacteria transcribe, duplicate and segregate their genomes all at once. Conflicts between DNA replication and active transcription are a major source of DNA damage and jeopardize genome integrity and cell survival. Co-orientation of replication forks and transcription units is thought to reduce the impact of such conflicts. Like transcription and replication, chromosome segregation relies on the translocation of multi-subunit protein complexes along DNA. Here, I highlight recent advances in our understanding of two major classes of structural maintenance of chromosomes (SMC) complexes in bacteria: Smc-ScpAB, whose DNA translocation is co-oriented with DNA replication by specific start sites, and MukBEF, which apparently lacks such co-ordination. Potential advantages of centralized and decentralized approaches to chromosome organization are discussed.