Many thanks for your help. Would you please let me know: what does 5x buffer mean, does it contain half of what the 10x buffer has? I have only 10x buffer, how could i make 10x into 5x buffer? Fei Xie MD feixie3 at sina.com Research Labs Fuzhou General Hospital China <http://www.biowww.net/forum/read.php?f=1&i=2746&t=2746>