[대학원 생명과학과 세미나 안내]
연사 : 류제경 박사(TU Delft)
연제 : Condensin is for DNA loop extrusion, but cohesin is for phase-separation
일시 : 2019년 10월 7일 (월) 오후 5시
장소 : 하나과학관 A동 109호
초청교수 : 이은진 교수
Abstract
Structural Maintenance of Chromosome (SMC) protein complexes are the key organizers of the spatiotemporal structure of chromosomes. The condensin SMC complex, which compacts DNA in mitosis, was recently shown to be a molecular motor that extrudes large loops of DNA. Also, the cohesin SMC complex has been suggested a DNA loop-extruding enzyme. The mechanism of the condensin, which takes large steps along DNA at low ATP consumption, remains elusive. In addition, in the case of cohesin, there has been no in vitro evidence of ATP-dependent DNA loop extrusion activity. Here, we use atomic force microscopy (AFM) and single-molecule fluorescence assay to test DNA loop extrusion activity of both condensin and cohesin complexes. We find that the yeast condensin complex extrudes a DNA loop, but the yeast cohesin complex does not induce DNA loop extrusion. Condensin is found to exhibit mainly O-shapes and B-shapes, and it toggles dynamically between these two states over time using high-speed AFM (HS-AFM). Condensin binds double-stranded DNA via a heat domain and, surprisingly, also via the hinge domain. For DNA loops, we observe a single condensin complex at the stem each loop, where the neck size of the DNA loop correlates with the width of the condensin complex. Our results suggest that condensin extrudes DNA by a cyclic fast switching of its conformation between the O and B shapes, consistent with a scrunching model. However, we find that cohesin SMC complex works differently from condensin, and this complex phase separates which might be related to heterochromatin formation.