Assays for the Interferon-Induced Enzyme 2′,5′ Oligoadenylate Synthetases

: Inhibition of protein synthesis by interferon treatment is mediated by two major pathways: the 2'-5'-linked oligoadenylates [2-5 (A)] synthetase-RNase L pathway and the double-stranded ribonucleic acid-dependent protein kinase-mediated pathway. 2-5 (A) synthetases are unique interferon-inducible enzymes that, upon activation by double-stranded RNA, polymerize adenosine triphosphate (ATP) to 2-5 (A) synthases. These 2-5 (A) synthetases bind and activate the latent RNase L, causing RNA degradation. In addition to the three major size classes of enzymatically active oligoadenylate synthetase proteins, at least one inactive oligoadenylate synthetase is known in human and mouse. Structure-function studies and recent crystal structure determination have identified several distinct sites in these proteins responsible for different biochemical functions. RNase L is the only known protein that binds to 2-5 (A) synthetases with very high affinity. Gene knockout studies of RNase L have identified its role in antiviral actions of interferon and in apoptosis. Recently, it has also been implicated in prostate cancer metastasis. In this chapter we describe several methodologies for studying biochemical and physiological properties of the 2-5 (A) synthetase-RNase L pathway.