Fig. 3. RNA-binding specificity of hRUL138. The same wild-type and K4^- variant hRUL138 fragments as in Fig. 2 were expressed as pET30 linker fusions and processed as before for Northwestern blotting, except that RNA probes derived from a different part of the HBV genome (panel HBV-RT) or an unrelated RNA derived from the alfalfa mosaic virus leader RNA (panel AMV) were used as probes. Loading was controlled by reprobing the blots with an anti-His antibody. Note that weak but detectable signals were also observed in the Northwestern blot lanes containing the K4^- mutant proteins.