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Activities of Bacterial Condensins for Chromosome Management in Pseudomonas aeruginosa

SMC (Structural Maintenance of Chromosomes) proteins are highly conserved and nearly ubiquitous in living organisms. They have a variety of critical functions in managing and processing chromosomes in all domains of life.

Eukaryotic organisms require multiple SMC complexes (cohesin, condensin and SMC5/6 complex) for mitotic chromosome condensation, sister chromatids cohesion and higher order folding of chromatin interphase.
In bacteria, three different SMC complexes (Smc-ScpAB, MukBEF, MksBEF) defined as bacterial condensins play an important role for chromosome organization and segregation. Recent advances in the understanding of SMC complexes activity revealed how they may drive 3D chromosome organization and compaction through a loop extrusion mechanism. The ability for SMC complexes to interact at various loci and to extrude DNA into loops may provide a universal unifying principle for chromosome management and processing.
Three types of structurally related SMC complexes, referred to as condensins, have been identified in bacteria. Smc-ScpAB is present in most bacteria while MukBEF is found in enterobacteria and MksBEF is scattered over the phylogenic tree. The contributions of these condensins to chromosome management were characterized in Pseudomonas aeruginosa that carries both Smc-ScpAB and MksBEF. In this bacterium, SMC-ScpAB controls chromosome disposition by juxtaposing chromosome arms. In contrast, MksBEF is critical for chromosome segregation in the absence of the main segregation system and affects the higher-order architecture of the chromosome by promoting DNA contacts in the megabase range.

A functional hierarchy rules bacterial condensin activity on the same DNA molecule

Strikingly, our results reveal a prevalence of Smc-ScpAB over MksBEF involving a coordination of their activities with chromosome replication. They also show that Escherichia coli MukBEF can substitute for MksBEF in P. aeruginosa while prevailing over Smc-ScpAB. Altogether, our results reveal a hierarchy between activities of bacterial condensins on the same chromosome.

Reference :
Distinct Activities of Bacterial Condensins for Chromosome Management in Pseudomonas aeruginosa
Lioy et al. (2020) Cell Reports, 33 : 108344
Doi : 10.1016/j.celrep.2020.108344

Contact :
Isabelle Vallet
Frédéric Boccard

par Communication - publié le