Nucleoside triphosphate-dependent DNA-binding properties of mos protein

We have previously shown that the mos gene product, p40(mos), produced in Escherichia coli binds ATP and has ATPase activity. In the present study, we investigated the DNA-binding properties of p40(mos) and two mos deletion mutant proteins. Nitrocellulose blot protein-DNA binding assays showed that p40(mos) binds DNA in the presence of Mg²⁺-ATP and certain other nucleoside triphosphates. Ninety percent of the p40(mos)-bound DNA is dissociated if the complex is washed in the presence of 1 M NaCl or in the absence of ATP. p40(mos)-DNA binding is not observed in the presence of AMP or the nonhydrolyzable ATP analog adenosine 5'-[β,γ-methylene]triphosphate; however, in the presence of ADP, p40(mos) binds DNA at 20% of the level that is observed with ATP. An N-terminal-deletion mutant protein, p19(mos), has no DNA-binding activity, whereas a C-terminal-deletion mutant protein, p25(mos), does. p25(mos) contains the ATP-binding domain, binds DNA in the presence of either ADP or ATP, and shows 5% and 45% binding (relative to that in the presence of ATP) in the presence of AMP and adenosine 5'-[β,γ-methylene]triphosphate, respectively. These results suggest that the N-terminal domain of p40(mos) is responsible for nucleoside triphosphate-mediated DNA binding. We also observed differential histone-DNA binding in the presence and absence of ATP.