Functional analysis of the baculovirus host range gene, hrf-1

The hrf-1 gene from Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) prevents translation arrest and promotes Autographa californica multiple nucleopolyhedrovirus (AcMNPV) replication in IPLB-Ld652Y cells (Ld652Y), a non-permissive L. dispar cell line. There are no motifs in the predicted protein sequence to suggest how it might function and the only homolog identified is encoded by another baculovirus, Orgyia pseudotsugata multiple nucleopolyhedrovirus (OpMNPV). In this study, we report a functional analysis of the hrf-1 protein. AcMNPV bearing carboxy- or amino-terminally truncation hrf-1, and hrf-1 mutated by two-amino acid insertions did not replicate Ld652Y cells. Neither OpMNPV hrf-1 nor an OpMNPV/LdMNPV chimeric hrf-1 supported AcMNPV replication. Mutations in a highly acidic domain of hrf-1, in which aspartic acid residues were replaced with alanine, had varied effects on hrf-1 function. They had no effect, abolished hrf-1 function completely, or partially supported protein synthesis in infected Ld652Y cells. A slight increase in protein synthesis was achieved by increasing the expression of hrf-1 acidic domain mutant proteins. Together, these results indicate a critical role for hrf-1 structure and suggest a functional role for the acidic domain.