FIG. 4.
Analysis of the site of action of nuclear extract by order of addition. Two orders of addition were compared: (i) addition of nuclear extract to salt-stripped PICs and then addition of target DNA (lanes 2 to 4) or (ii) addition of nuclear extract to target DNA and then addition of salt-stripped PICs (lanes 5 to 7). The amounts of nuclear extract added per reaction mixture are indicated above the autoradiogram. Lane 1 (Buffer) contained no added protein. The amounts of reactants were as follows: φX174 DNA, 2.6 × 10−9 M; HMG I(Y) in 10 μl of nuclear extract, 1.1 × 10−8 M; and cDNA in PICs, 8.3 × 10−13 M. The number of binding sites for HMG I(Y) in φX174 DNA is not known but is likely to be large.