A comparison of the protective effect against Mengo virus infection in mice of interferons induced by polyI:C and Mengo virus

PolyI: C (complexed polyinosinic and polycytidylic acids) has been demonstrated to protect mice against infection with lethal doses of a highly virulent mutant of Mengo virus. However, the serum interferon titers it induced were considerably lower and of much shorter duration than the interferon titers induced by infection with the Mengo virus mutant. Evidence has been obtained that the interferon induced by polyI: C is as effective against Mengo virus infection as polyI: C itself. It has also been shown that, unit for unit (measured by the plaque reduction of vesicular stomatitis virus), the polyI: C-induced interferon is much more effective against Mengo virus infection than the Mengo virus-induced interferon itself.

Specific interaction of tRNA 3'-terminal nucleotidyl transferase with polynucleates

E. coli tRNA lacking one or more of the 3′-terminal bases was prepared for use in the tRNA 3′-terminal nucleotidyl transferase system, by periodate–amine cleavage or by snake venom phosphodiesterase treatment. Optimal conditions for the transferase reaction with tRNA-pC and tRNA-pCpC and for detection of complexing of various nucleic acids to transferase were determined.Although R17 RNA-pC, R17 RNA-pCpC, and synthetic polynucleotides are unable to accept nucleoside monophosphates in the enzymic reaction, it was found that they are able to form complexes with the enzyme. The extent of binding depends inversely on the degree of base stacking in the synthetic polynucleotide. In keeping with this, melting of tRNA reduces both the CMP-accepting activity and the binding capacity. In competition studies, it was found that R17 RNA and tRNA compete with one another for binding, and that R17 RNA and to lesser extents, poly-U and poly-A, inhibit the transferase reaction with tRNA. Thermal studies, however, show that only tRNA can protect the enzyme from heat inactivation. These findings suggest that the recognition process for transferase and its nucleic acid substrate involves at least a two-step interaction. First, there is nonspecific binding which is followed by specific complex formation, an event which depends on the specific structure of tRNA.