The protein concentration of the samples was measured with the method of Bradford (29) and the amounts of sample loaded on to the SDS-PAGEs are those indicated. The quantification of the bands identified by western blot was performed by using the program Quantity One 4.4.0 in a ChemiDoc EQ System (Bio-Rad, Hercules, CA, USA) with the volume analysis tool. The frameshifting efficiency was calculated as the ratio of the intensity of the bands of the frameshifted product/frameshifted product + termination product.