C-JUN STIMULATES ORIGIN-DEPENDENT DNA UNWINDING BY POLYOMAVIRUS LARGET-ANTIGEN

The AP1 protein c-Jun has previously been shown to stimulate polyomavi rus (Py) DNA replication in vivo. In order to define the mechanism, ry e added purified c-Jun protein to the origin-dependent and large T ant igen (LT)-dependent in vitro DNA unwinding assay. c-Jun protein was fo und to stimulate by similar to 5-fold the unwinding of a 290 bp linear DNA fragment containing both the Py origin and the AP1 recognition se quence to which c-Jun binds, Efficient levels of stimulation were spec ifically observed at limiting concentrations of LT for unwinding. Unde r similar conditions, PS DNA replication was stimulated to a comparabl e extent by AP1 in a purified in vitro replication assay. Mobility shi ft and DNase I footprinting assays showed that c-Jun stimulates the AT P-dependent binding of LT to the origin core by similar to 7-fold. Fur thermore, c-Jun was found to interact directly with LT, but not with r eplication protein A. The activities of c-Jun to stimulate unwinding a nd origin binding of LT were found to be harbored within the N-termina l region of c-Jun, which is distinct from the DNA binding domain, We s peculate that certain transcription factors may possess specific DNA r eplication domains that function to stimulate the loading of replicati on factors at the origin during the initiation of DNA synthesis.