Mechanism of The Activation of 2'-5'Oligoadenylate Synthetase by Double-Stranded RNA

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1. Nature of mouse 2'-5'oligoadenylate synthetase (2-5AS)The ORF of mouse 2-5AScDNA encodes 367 amino acid residues (42kD) , and two subtypes (S^+ and S^-) of the cDNA have been isolated, which are different in 14 amino acids. The enzymatic activity of S^- is only about 1/1000 of that of S^+, while the S^-mutant, whose 176Trp is converted to 176Glu, has an increase of activity by 30 times of that of S^-. The S^+ enzyme had a higher binding activity to double stranded RNA comparing with S^-, but the S^- mutant had a similar activity to S^+. These results indicate that the structure of the central part of the enzyme is responsible both to the enzyme activity and to the binding to double stranded RNA.2. Physiological expression of the 2-5AS gene in mouse intestineThe normal mouse, not treated exogenously with any IFN of IFN inducers, has been shown to have an enhanced level of 2-5AS activity. Among the organs of normal mouse, intestinal tissues had the highest levels of 2-5AS mRNA.Furthermore, the 42kD 2-5AS mRNA was expressed in intestines from germ-free mice and fetuses. Immunoblotting analysis using a monoclonal antibody against the 42kD 2-5AS revealed that the 42kD enzyme as well as a cross-reactive protein of 30kD were produced in the organs of normal mouse.