Poly , binding actinomycin

The binding of actinomycin D to calf thymus DNA (0.01M, 0.1M, and 0.2M NaCl) and to poly(dGdC) poly(dGdC) (0.1M NaCl) (Figure 4) was also examined by phase partition techniques. For both DNAs, a cooperative process was seen. In the case of calf thymus DNA, the decreasing salt concentration appears to Increase the degree of cooperativity. 

This data is consistent with a model in which daunorubicin is bound to Isolated DNA binding sites and dissociates with its normal lifetime of 0.2 sec. Whereas daunorubicin and actinomycin D molecules, residing at "adjacent sites", dissociate with a time constant of approximately 5 sec. These results are indicative of a cooperative interaction between daunorubicin and actinomycin D when the two are bound to poly(dAdT).poly(dAdT). 

An interesting aspect of the facilitated binding of actinomycin D to poly(dA-dT) -poly(dA-dT) is the question of whether the bound actinonQ cin D would Inhibit RNA polymerase, since it has been well documented that actinomycin D very effectively inhibits RNA polymerase... 

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