Detection of small lacZ gene-specific RNA. Total RNA was isolated from Drosophila cell cultures and fractionated by chromatography using sepharose CL-2B agarose (Sigma) in Micro Bio-Spin columns (Bio Rad). Fractionated samples were analysed in 15% polyacrylamide-UREA gels and stained with ethidium bromide before the RNA species were transferred to Hybond N+ membrane (Amersham) by electroblotting. The membrane was probed with an antisense digoxigenin-labelled lacZ transcript corresponding to ~500 nt at the 5' end of the lacZ gene. The upper panel shows the small RNA species detected by probing with a lacZ gene-specific probe in DS2 cells (lanes 1, 2), DS2-HC-Pro cells (lanes 3, 4), DS2-2b cells (lanes 5, 6) and DS2-16k cells (lanes 7, 8). Cells represented in lanes 1, 3, 5 and 7 were transfected with pMT/V5-His/lacZ and those represented in lanes 2, 4, 6 and 8 were transfected with pMT/V5-His/lacZ and dsRNA. The line to the right indicates the position of GFP specific siRNAs produced in plants as described by Canto et al. (47). The lower panel shows the RNA species detected by staining of the gel before electroblotting.