Novel reactions of RNAase P with a tRNA-like structure in turnip yellow mosaic virus RNA.

A quasi-continuous double hellix, containing a pseudoknot and ending in a single-stranded region which contains CCA, can be formed at the 3' terminus of the genomic RNAs of certain plant viruses. M1 RNA (the catalytic subunit) alone and the RNAase P holoenzyme from E. coli cleave the tRNA-like structure of TYMV RNA in vitro at the 5' side of the quasi-helical structure to generate 5' phosphate and 3' hydroxyl groups in the cleavage products. The intact pseudoknot structure in the substrate is not required for the reaction catalyzed by M1 RNA alone, but its presence markedly improves the efficiency of the reaction. In addition to its essential role in the biosynthesis of tRNA, RNAase P may have another function in vivo, namely, in the physiology of viral infections.