FIG. 5.

Binding of VIRP1 by plaque lift assay. Binding specificity of VIRP1 and PSTVd RNA was tested by plaque lift assay. A mixture (1:1) of λVIRP1 and λ-ZAPII phage was plated out and tested for binding with different RNAs. (A and B) Only when monomeric (A) or multimeric (B) PSTVd positive-strand RNA forms (for details see Materials and Methods) were used as RNA probes could positive signals be discriminated from those due to background. (C and D) When the same mixture was plated at a lower density of 25 PFU/plate and allowed to interact with either potato U1 RNA (C) or human U1 RNA (D), only background signals were visible. In panels C and D the numbers of signals visible on the autoradiograph were the same as the numbers of plaques per plate. The black arrows show the signals corresponding to VIRP1 plaques, which interact with PSTVd (positive signals), while the open arrows indicate the background signals.