The long isoform of ZAP coordinates multiple enzymes to mediate complete decay of target transcripts

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• Zinc-finger antiviral protein (ZAP) restricts viral replication via ZAP-mediated RNA decay (ZMD), particularly for viruses with CpG clusters.
• The differential antiviral activity of ZAP isoforms and their cofactor recruitment mechanisms for RNA decay remain unclear.

Purpose of the Study:

• To elucidate the ordered events of the ZAP-mediated RNA decay pathway.
• To understand how ZAP isoforms differ in viral RNA binding and cofactor recruitment.

Main Methods:

• Investigated ZAP isoform binding specificity to viral RNA.
• Identified key endoribonucleases and degradation factors involved in ZMD.
• Examined protein-protein interactions within the ZMD complex using RNase-resistant assays.

Main Results:

• The long ZAP isoform exhibits preferential binding to viral RNA with distinct motifs compared to the short isoform.
• Viral RNA is cleaved by KHNYN, followed by 3' uridylation (TUT4/TUT7) and degradation (DIS3L2) of the 5' fragment, and degradation of the 3' fragment by XRN1.
• ZAP and TRIM25 form RNase-resistant complexes with KHNYN, TUT7, DIS3L2, and XRN1, which are enhanced during viral infection.

Conclusions:

• The long ZAP isoform acts as a scaffold, recruiting essential enzymes to form an RNA decay complex on viral RNA.
• This mechanism effectively restricts viral replication by degrading viral RNA.
• The ZAP pathway also impacts cellular transcript levels during viral infection.