CLIP-seq of ZAP in HeLa CRISPR control and KHNYN knockout cells infected with CpG-recoded HIV-1

The zinc finger antiviral protein (ZAP, also known as PARP13 or ZC3HAV1) is an antiviral factor that restricts the replication of a wide range of RNA and DNA viruses. It exerts its antiviral function primarily by binding specific sequences known as ZAP response elements (ZREs) within single-stranded RNA, promoting RNA degradation or inhibiting its translation. The ZAP RNA-binding domain shows a high affinity for binding to CpG dinucleotides, which are generally depleted in vertebrate RNA viruses. There are two major isoforms of ZAP, the long isoform (ZAP-L) and the short isoform (ZAP-S). ZAP has no enzymatic activity and requires cofactors to effectively restrict viral replication. We aimed to characterise the mechanisms underlying ZAP-mediated RNA decay and, in particular, to investigate how ZAP cofactors influence its binding to viral RNA and subsequent RNA degradation. We used an HIV-1 model that was sensitised to ZAP activity by introducing 36 additional CpG dinucleotides through silent mutations into the env gene. The role of ZAP cofactors TRIM25 and KHNYN as well as the ZAP-L and ZAP-S isoforms was investigated by CRISPR-mediated depletion. ZAP interactions with viral RNA was analysed using iCLIP assays performed in TRIM25, KHNYN, ZAP-L and ZAP-S knockout cell lines. In addition, we used 3' and 5' RACE-seq in combination with Oxford Nanopore Technologies sequencing technology to accurately identify KHNYN-mediated cleavage sites on viral RNA.