Small interfering RN As (siRNAs) targeting the coding region of hepatitis A virus (HAV) were shown to specifically inhibit viral genome replication. Compared to the coding region, the HAV internal ribosomal entry site (IRES) in the 5' non-coding region is highly sequence-conserved and folds into stable secondary structures. Here, we report efficient and sustained RNA interference mediated by both RNase III-prepared siRNA (esiRNA) and vector-derived short hairpin RNAs (shRNAs) that are targeted to various domains of the HAV IRES. Using reporter constructs, and the DNA-based HAV replicon system, we found that shRNAs targeting the HAV IRES domains IIIc and V sustainably suppressed genome translation and replication whereas the IRES domains IIIa and IV were resistant to RNA interference. Our study suggests that some HAV IRES domains might be used as a universal and effective target for specific inhibition of HAV infection. (c) 2005 Elsevier Inc. All rights reserved.