Effects of siRNA expression vectors on b PRNP. A and B, effects of different lengths of siRNAs expressed by different vectors. A: piGENE hU6-EGFP was a positive control siRNA vector for EGFP. Numerals after vectors indicate the lengths of siRNA; 19, 23, 25, 27, and 29 correspond to No. 6, 10, 12, 13, and 14 in Table 2, respectively. B: piGENE Fluc is a positive control siRNA vector against firefly luciferase. Numerals after vectors indicate the lengths of siRNA; 19, 20, 21, and 22 correspond to No. 6, 7, 8, and 9 in Table 2, respectively. C and D, effects of different target sites and expression vectors on siRNA activities. C: numerals after vectors indicate the start sites of siRNA; 132, 372, 616, and 725 correspond to No. 2, 4, 9, and 16 in Table 2, respectively. D: as for numerals after vectors, see the legend to C. E: comparison of vector activities. Vectors expressed 19 mer, and the sequence corresponds to No. 6 in Table 2.