Northern blot for Dicer products. Total RNA from: lane 1, HeLa cells; lane 2, HeLa cells overexpressed with S-AS mRNA; lane 3, HeLa cells transfected with IVT-overlap dsRNA; lane 4, HeLa cells overexpressing hairpin S-AS RNA; lane 5, marker. The vector based RNA (1,100 bp) band in lanes 2 and 4 represent mRNA originating from the vector. The overlap region (200 bp) band in lane 3 is the transfected overlap RNA, and the same band in lane 4 could represent an intermediate product from siRNA production or a byproduct of the cell interferon response. The Dicer product (approximately 20 bp) band represents 21 nucleotide RNA sequences, characteristic of RNAse III enzyme products.