Autographa californica nucleopolyhedrovirus (AcMNPV), the type member of the virus family Baculoviridae, infects pest insects and has been the subject of many studies for its development as a biopesticide. It is also the virus upon which most of the commercial baculovirus protein expression systems are based. AcMNPV infection of cultured host Spodoptera frugiperda (Sf9) cells can induce a number of alterations of host cell properties including altering the cellular cytoskeleton, an arrest of the cell cycle in G 2 /M, and the global shutoff of host protein translation. Additionally, several cellular transcripts have been shown to be down-regulated following AcMNPV infection. In this study, we take a differential display approach to address whether a global down-regulation of Sf9 host transcripts occurs at late times of infection. Additionally, we also use this approach to search for host mRNAs which are up-regulated at early times of infection, and may be important for facilitating baculovirus infection. From these experiments we can confirm a global down-regulation of Sf9 mRNA levels at late times of infection. We also found that up-regulation of individual host gene RNA levels at early times of infection did not occur frequently. One host transcript which was found to be transiently up-regulated as a result of AcMNPV infection was an Sf9 Hsc70 gene. Hsc70 proteins have been shown to play a vital role in the life-cycle of other large DNA viruses, which suggests that this protein is also important for baculovirus infection.

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We characterized tellina virus 1 (TV-1), a birnavirus isolated from the marine bivalve mollusk Tellina tenuis. Genome sequence analysis established that TV-1 is representative of a viral cluster distant from other birnaviruses. The maturation process of the polyprotein encoded by the genomic segment A was delineated with the identification of the N-termini of the viral protease VP4 and the ribonucleoprotein VP3, and the characterization of peptides deriving from the processing of pVP2, the VP2 capsid protein precursor. One of these peptides was shown to possess a membrane-disrupting domain. Like the blotched snakehead virus, the polyprotein exhibits a non-structural polypeptide (named [X]) located between pVP2 and VP4. Mutagenesis analysis allowed the identification in VP4 of a catalytic Ser-Lys dyad that does not possess the common Gly-X-Ser signature of the serine hydrolases. The genomic segment B encodes the viral RNA-dependent RNA-polymerase VP1 with the unique sequence motif arrangement identified in other birnavirus VP1s.

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