LOSS OF DNA-BINDING AND NEW TRANSCRIPTIONAL TRANSACTIVATION FUNCTION IN POLYOMAVIRUS LARGE T-ANTIGEN WITH MUTATION OF ZINC FINGER MOTIF

A putative zinc finger in polyomavirus large T-antigen was Investigated. We were unable to demonstrate unequivocally a requirement for zinc in specific DNAbinding using the chelating agent 1,10-phenarrthroline. An involvement of the putative zinc finger in specific DNA-binding was nevertheless suggested by the properties of a mutant protein with a cysser replacement in the finger motif. Probably as a result of the defective DNA-binding, the mutant protein had lost its activity in initiation of viral DNA-replication and in negative regulation of viral early transcription. However, the frans-activation of the viral late promoter was normal. The analysis also revealed a previously unrecognized activity of large T-antigen. The mutant protein frans-activated the viral early promoter. In thewild-type protein this activity is probably concealed by the separate, negative regulatory function. © 1990 Oxford University Press.