[Interaction of SV40 T-antigen with homologous and heterologous DNA].

: Using the DNA filter binding assay, the effects of ionic strength and pH on SV40 T-antigen interaction with viral DNA were studied. The apparent association constants for T-antigen binding to SV40 DNA in Scatchard coordinates in the presence of 40 mM NaCl are equal to 0.67 . 10(6) M-1 (pH 6.0) and 0.86 x 10(7) M-1 (pH 7.4). These data indicate that the interaction between T-antigen and SV40 DNA is more specific at pH 7.4. The coincident values of association constants for T-antigen binding to viral and cellular DNAs (Ka = 0.9 x 10(7) M-1 for cellular DNA) at pH 7.4 and the absence of competition between the two DNA species upon binding with T-antigen suggest that viral and cellular DNAs possess similar sites for T-antigen binding. Denatured DNA competes with viral DNA only at pH 6.0, when the T-antigen--SV40 DNA interaction is less specific.