Biological, biochemical, and physicochemical evidence for the existence of the polyadenylic-polyuridylic-polyinosinic acid triplex.

When primary rabbit kidney cell cultures are treated with either polyadenylic acid-polyuridylic acid or polyadenylic acid-polyribothymidylic acid (poly(rT)) and then judiciously exposed to actinomycin D and cycloheximide, high titers of interferon are found in the extracellular medium ("superinduction") (Vilcek, J. (1970) Ann. N. Y. Acad. Sci. 173, 390-403; Tan, Y. H., Armstrong, J. A., Ke, Y. H., and Ho, M. (1970) Proc. Natl. Acad. Sci. U. S. A. 67, 464-471). If polyinosinic acid is added 1 hour prior to, simultaneously with, or 1 hour after the active interferon inducers, dramatic reductions in interferon production from the "superinduced" cells result. Based on experiments involving sucrose gradient ultracentrifugation, pancreatic ribonuclease A resistance, ultraviolet mixing curves, and ultraviolet absorbance-temperature profiles, the explanation for this phenomenon was determined to be the formation of polynucleotide triplexes in the following way: poly(A)-poly(U) + poly(I) yields poly(A)-poly(U)-poly(I)poly(A)-poly(rT) + poly(I) yields poly(A)-poly(rT)-poly(I). In addition, based on similar methodology, the following reactions involving these triplexes were demonstrated: poly(A)-2 poly(I) + poly(U) yields poly(A)-poly(U)-poly(I) + poly(I)poly(A)-2 poly(I) + poly(rT) yields poly(A)-poly(rT)-poly(I) + poly(I)POLY(A)-2 poly(I) + 2 poly(U) yields poly(A)-2 poly(U) + 2 poly(I) and POLY(A)-poly(U)-poly(I) + poly (U) yields poly(A)-2 poly(U) + poly(I).