The molecular basis of KAP1-dependent transcriptional silencing (360G-Wellcome-109077_B_15_A)

The transcriptional regulator KRAB-associated protein 1 (KAP1) is crucial for preserving genome integrity by repressing potentially harmful retroelements. Following its recruitment to retrotransposons by KRAB domain containing zinc finger proteins (KRAB-ZFPs), KAP1 coordinates the assembly of a repressor complex containing the histone methyltransferase SETDB1 and histone deacetylase 1 (HDAC1) to induce epigenetic silencing of these elements. In addition to its role in repressing transposons, KAP1 also regulates the expression levels of numerous other genes. Interestingly, the transcriptional activities of KAP1 can be strongly influenced by posttranslational modifications (PTMs). Most notably, phosphorylation at S473 and phosphorylation at S824 both significantly alleviate the repression mediated by KAP1. The molecular mechanisms underlying these processes, however, remain poorly understood. To elucidate the structural basis of KAP1-dependent transcriptional repression, we will reconstitute a complex consisting of KAP1, SETDB1, the KRAB-ZFP ZNF93 and a DNA fragment containing the recognition sequence for ZNF93. Subsequently, we use single-particle cryo-EM to determine the structure of this complex. In addition, we will investigate the mechanism by which PTMs regulate the transcriptional activities of KAP1. Our central objective in this context will be determining how phosphorylation at S473 or S824 results in transcriptional activation.