Protein-protein interactions play important role in cell biochemistry by fa
vorably or adversely influencing major molecular events. In most documented
cases, the interaction is direct between the partner molecules. Influence
of activity in the absence of direct physical interaction between DNA trans
action proteins is another important means of modulation. We show here that
single strand binding protein stimulates DNA topoisomerase I activity with
out direct protein-protein interactions. The stimulation is specific to top
oisomerase I, as DNA gyrase activity is unaffected by SSB. We propose that
such cases of functional collaboration between DNA transaction proteins pla
y important roles in vivo. (C) 2001 Academic Press.