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Publication Abstract from PubMed

Structural maintenance of chromosome (SMC) complexes fold DNA by loop extrusion to support chromosome segregation and genome maintenance. Wadjet systems (JetABCD/MksBEFG/EptABCD) are derivative SMC complexes with roles in bacterial immunity against selfish DNA. Here, we show that JetABCD restricts circular plasmids with an upper size limit of about 100 kb, whereas a linear plasmid evades restriction. Purified JetABCD complexes cleave circular DNA molecules, regardless of the DNA helical topology; cleavage is DNA sequence nonspecific and depends on the SMC ATPase. A cryo-EM structure reveals a distinct JetABC dimer-of-dimers geometry, with the two SMC dimers facing in opposite direction-rather than the same as observed with MukBEF. We hypothesize that JetABCD is a DNA-shape-specific endonuclease and propose the "total extrusion model" for DNA cleavage exclusively when extrusion of an entire plasmid has been completed by a JetABCD complex. Total extrusion cannot be achieved on the larger chromosome, explaining how self-DNA may evade processing.

DNA-measuring Wadjet SMC ATPases restrict smaller circular plasmids by DNA cleavage.,Liu HW, Roisne-Hamelin F, Beckert B, Li Y, Myasnikov A, Gruber S Mol Cell. 2022 Dec 15;82(24):4727-4740.e6. doi: 10.1016/j.molcel.2022.11.015. PMID:36525956^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.