ssDNA-dsRNAs are cleaved at the next to its chimera-junction point by an unknown RNase activity

► ssDNA-dsRNA chimeras are cleaved in a position-specific manner in serum. ► The cleavage site is at the phosphodiester linkage between the first and second RNA. ► 2′ methoxylation of the first RNA prevents the cleavage. ► This activity of RNase may be related to siRNA defense system.