TARGETED MUTAGENESIS OF THE HUMAN PAPILLOMAVIRUS TYPE-16 E2 TRANSACTIVATION DOMAIN REVEALS SEPARABLE TRANSCRIPTIONAL ACTIVATION AND DNA-REPLICATION FUNCTIONS

The E2 gene products of papillomavirus play key roles in viral replica tion, both as regulators of viral transcription and as auxiliary facto rs that act with E1 in viral DNA replication, We have carried out a de tailed structure-function analysis of conserved amino acids within the N-terminal domain of the human papillomavirus type 16 (HPV16) E2 prot ein. These mutants were tested for their transcriptional activation ac tivities as well as transient DNA replication and E1 binding activitie s, Analysis of the stably expressed mutants revealed that the transcri ptional activation and replication activities of HPV16 E2 could be dis sociated. The I73A mutant was defective for the transcriptional activa tion function but retained wild-type DNA replication activity, whereas the E39A mutant had wild-type transcriptional activation function but was defective in transient DNA replication assays, The E39A mutant wa s also defective for HPV16 E1 binding in vitro, suggesting that the ab ility of E2 protein to form a complex with E1 appears to be essential for its function as an auxiliary replication factor.