bioRxiv preprint doi: https://doi.org/10.1101/505677; this version posted December 25, 2018. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. Structure of the tripartite motif of KAP1/TRIM28 identifies molecular interfaces required for transcriptional silencing of retrotransposons Guido A. Stoll1, Shun-ichiro Oda1, Zheng-Shan Chong1, Minmin Yu2, Stephen H. McLaughlin2 and Yorgo Modis1,* 1 Molecular Immunity Unit, Department of Medicine, University of Cambridge, MRC Laboratory of Molecular Biology, Cambridge Biomedical Campus, Cambridge, CB2 0QH, UK 2 MRC Laboratory oF Molecular Biology, Cambridge Biomedical Campus, Cambridge, CB2 0QH, UK * Correspondence:
[email protected] (Y.M.) Abstract Transcription oF transposable elements is tightly regulated to prevent damage to the genome. The family of KRAB domain-containing zinc Finger proteins (KRAB-ZFPs) and KRAB-associated protein 1 (KAP1/TRIM28) play a key role in regulating retrotransposons. KRAB-ZFPs recognize speciFic retrotransposon sequences and recruit KAP1, which controls the assembly of an epigenetic silencing complex including histone H3K9 methyltransferase SETDB1. The chromatin remodeling activities of this complex repress transcription of the targeted transposable element and any adjacent genes. Here, we use biophysical and structural approaches to show that the tripartite motif (TRIM) of KAP1 Forms antiparallel dimers, which Further assemble into tetramers and higher-order oligomers in a concentration-dependent manner. Structure-based mutations in the B-box 1 domain prevented higher-order oligomerization without a signiFicant loss oF retrotransposon silencing activity in a cell-based assay, indicating that, in contrast to other TRIM family members, selF-assembly is not essential For the function of KAP1.