tokens: Fifteen microliter binding reactions were prepared , each consisting of 20 000 c . p . m . radiolabeled DNA probe , 5 micro g of crude protein extract , non - specific competitor DNAs ( 0 . 3 micro g of yeast tRNA , 0 . 3 micro g of salmon sperm DNA and 0 . 5 micro g of E . coli DNA ) , 10 micro g of BSA , 10 mM Tris - HCl ( pH 8 . 0 ) , 10 mM MgCl2 and 8 % glycerol .