Oral Presentation 41st Lorne Genome Conference 2020

Curious in the nucleus: Cryo-EM of telomeres and rChIP of chromatin binders (#24)

Thomas Cech 1 2 3 , Ci Ji Lim 1 2 3 , Yicheng Long 1 2 3 , Taeyoung Hwang 1 2 3 , Arthur J Zaug 1 2 3 , Anne R Gooding 1 2 3 , Karen J Goodrich 1 2 3 , Alexandra T Barbour 3 , Allison E McKay 1 2 3 , John L Rinn 1 2 3 , Deborah S Wuttke 3
  1. BioFrontiers Institute, University of Colorado, Boulder, CO, USA
  2. Howard Hughes Medical Institute, University of Colorado, Bouler, CO, USA
  3. Department of Biochemistry, University of Colorado, Boulder, CO, United States

The human CST (CTC1-STN1-TEN1) protein complex functions at telomeres to promote the switch from telomerase extension of the G-strand to synthesis of the C-strand DNA. It also works genome-wide to help resolve stalled replication forks. To provide a structural framework for understanding CST function, we have solved its structure at 2.95 Å by cryo-EM. Addition of telomeric ssDNA triggers the assembly of CST into a 2-megadalton decameric supercomplex. The decameric form of CST suggests the intriguing possibility of ssDNA architectural organization similar to what the nucleosome provides for dsDNA. Moving away from the telomere, formation of facultative heterochromatin requires the histone methyltransferase PRC2 (Polycomb Repressive Complex 2). We have developed rChIP (RNA-dependent Chromatin Immunoprecipitation) to test the importance of RNA in PRC2 binding to chromatin. We propose that PRC2 binds RNA, DNA, and K27me3-histone 3 marks, in that order, to localize to its sites of action.