Title: Studying Chromosome Conformation and Dynamics Using Chemically Induced Chromosomal Interaction (CICI)

Abstract: Chemically Induced Chromosomal Interaction (CICI) method developed in our lab enables induction of stable chromosome interactions. This method allows us to accurately measure the encounter time, or the “first passage time (FPT)” of two targeted loci on the chromosome. Here, we extracted the FPTs from different loci pairs in G1-arrested cells and uncovered distinct patterns for inter- and intra-chromosomal interactions. Specifically, we found that intra-chromosomal pairs with comparable physical distances formed contacts more rapidly than inter-chromosomal pairs, despite exhibiting similar diffusion rates. This difference in distance dependencies indicates an active mechanism that promotes intra-chromosomal interaction. Through targeted depletion experiments, we identified condensin, but not cohesin, as the key factor driving the short encounter time observed in intra-chromosomal loci. A polymer model based on these data suggests that condensin extrudes loops at low frequency but with high speed and long processivity. Overall, these findings reveal a new role of condensin in regulating interphase yeast genome and provide insight into the searching mechanism of cis-regulatory elements for their targets in vivo.

Host: Xingcheng Lin