I have approx 3000base ssDNA (3'-5', synthesized by asymmetric PCR) and complementary RNA (5'-3' ; synthesized by T7-transcription). I want to prepare DNA-RNA helix (hybrid) in solution. I have tried with buffer containing 40mM PIPES (6.5pH), 400mM NaCl and 1mM EDTA supplemented with 50% formamide at room temperature for 1 hr using equimolar concentrations of RNA/ssDNA. But it was not successful. Could you please give some suggestions. Thank you.