Characterization of a viroid-derived RNA promoter for the DNA-dependent RNA polymerase from Escherichia coli.

This paper attributes a novel function, namely, that of transcriptional promoter, to the self-complementary, self-cleaving hammerhead RNA sequences found in RNA derived from the peach latent mosaic viroid (PLMVd). The features of this RNA promoter, which adopts a hairpin structure that can be utilized by Escherichia coli RNA polymerase (RNAP) for in vitro transcription, that trigger the RNAP driven transcription and are responsible for the specific initiation of synthesis are described. The essential requirement for initiation is a basepaired uridine adjacent to the loop. The presence of a loop composed of at least six nucleotides connected to a relatively unstable stem significantly increases the level of initiation. Finally, we present several insights into the mechanism of the RNAP which reveal that it behaves differently with an RNA template as compared to a DNA one.