The Cleveland Clinic Foundation

Bret A Hassel

Robert H Silverman

Aimin Zhou

Isolated 2-5A-dependent RNases, an interferon-induced enzyme which is activated by 5'-phosphorylated, 2',5'-linked oligoadenylates (2-5A) and implicated in both the molecular mechanisms of interferon action and in the fundamental control of RNA stability in mammalian cells, and encoding sequences therefor are disclosed. The expression cloning and analysis of murine and human 2-5A-dependent RNases is also disclosed. Recombinant human 2-5A-dependent RNase produced in vitro bound an activating affinity matrix, 2-5A-cellulose, resulting in ribonuclease activity. The 2-5A binding properties of the recombinant and naturally occurring forms of 2-5A-dependent RNase are basically identical. Interferon induction of 2-5A-dependent RNase expression is demonstrated by measuring the mRNA levels in cells treated with interferon and cycloheximide. Analysis of aligned murine and human 2-5A-dependent RNase sequences revealed several features, including similarity to RNase E which is implicated in the control of mRNA stability in E. coli. A duplicated phosphate-binding loop motif is determined by deletion analysis and site-directed mutagenesis to function in the binding of 2-5A.

Animal 2-5A dependent RNases

2-5A-dependent RNase, an endoribonuclease that requires 5'-phosphorylated 2',5'-linked oligoadenylates (2-5A), functions in the molecular mechanism of interferon action. Recombinant, 2-5A-dependent RNase was expressed to high levels (at least 10% of the soluble protein) in insect cells by infecting with baculovirus containing human cDNA to 2-5A-dependent RNase. In contrast, there was no 2-5A-dependent RNase present in control insect cells infected with nonrecombinant baculovirus. The purified, recombinant enzyme eluted from a gel-filtration column as a monomer that showed potent and highly specific, 2-5A-dependent RNase activity. Precise activitor requirements were determined using the purified enzyme of a variety of 2',5'-linked oligonucleotides. The activated enzyme was capable of cleaving both poly(rU) and, to a lesser extent, poly(rA) but not poly(rC), poly(rG), or poly(dT. Interestingly, poly(rU) was cleaved to a series of discrete products ranging between 5 and 22 nucleotides in length. Furthermore, whereas manganese and magnesium stimulated 2-5A-dependent RNase activity, the enzyme was capable of cleaving RNA in the absence of divalent cations.

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Chagrin Falls, OH, United States of America

Bret A Hassel