Hello Amanda and Alan, I'm not sure on the subject but read a good article in Biosystems Reporter issue 23. oct 94 by Perkin and Elmer Maybe they could help you Applied Biosystems Ltd Kelvin Close, Birchwood Science Park North, Warrington, Cheshire,WA3 2BR The article talks about a Dr Saul Silverstein from Columbia University. Hope this helps, Emma Dalton.