Functional dissection of the baculovirus late expression factor-8 gene: sequence requirements for late gene promoter activation.

The late expression factor-8 gene (lef-8) of Autographa californica M nucleopolyhedrovirus encodes the largest subunit of the virally encoded DNA-directed RNA polymerase specific for the transcription of late and very late viral genes. The sequence of lef-8 predicts a C-terminal motif of 13 amino acids that is conserved in other polymerases. Detailed mutagenesis throughout lef-8 was performed, including this C-terminal motif, to define sequences required for late promoter activation. It was found that the conserved C-terminal motif was critical for late gene expression. In addition, regions throughout the entire lef-8-encoding sequence were important for optimal function, suggesting complex protein-protein and protein-DNA interrelationships in the late gene-specific viral transcriptosome.