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Mol Cell. 2017 Mar 2;65(5):861-872.e9. doi: 10.1016/j.molcel.2017.01.026. Epub 2017 Feb 23.

Tuned SMC Arms Drive Chromosomal Loading of Prokaryotic Condensin.

Author information

1
Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
2
Department of Fundamental Microbiology, University of Lausanne, Bâtiment Biophore, 1015 Lausanne, Switzerland.
3
Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany; Department of Fundamental Microbiology, University of Lausanne, Bâtiment Biophore, 1015 Lausanne, Switzerland. Electronic address: stephan.gruber@unil.ch.

Abstract

SMC proteins support vital cellular processes in all domains of life by organizing chromosomal DNA. They are composed of ATPase "head" and "hinge" dimerization domains and a connecting coiled-coil "arm." Binding to a kleisin subunit creates a closed tripartite ring, whose ∼47-nm-long SMC arms act as barrier for DNA entrapment. Here, we uncover another, more active function of the bacterial Smc arm. Using high-throughput genetic engineering, we resized the arm in the range of 6-60 nm and found that it was functional only in specific length regimes following a periodic pattern. Natural SMC sequences reflect these length constraints. Mutants with improper arm length or peptide insertions in the arm efficiently target chromosomal loading sites and hydrolyze ATP but fail to use ATP hydrolysis for relocation onto flanking DNA. We propose that SMC arms implement force transmission upon nucleotide hydrolysis to mediate DNA capture or loop extrusion.

KEYWORDS:

ParB; SMC; Smc/ScpAB; chromosome segregation; cohesin; coiled coil; condensin; heptad repeat; kleisin; periodicity

PMID:
28238653
PMCID:
PMC5344682
DOI:
10.1016/j.molcel.2017.01.026
[Indexed for MEDLINE]
Free PMC Article

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