known function
The gene ac154 encodes a protein (calculated mass 9.4 kDa, 81 aa) with unknown function. Transcripts of this gene have been identified (287). Only four homologs are present in other Alphabaculoviruses (Table 2).
The research towards elucidating the function of AcMNPV genes started in the early 1980s with the assignment of polyhedrin and p10, but was enhanced by the publication of the complete genome sequence in 1994 showing originally 154 ORFs (9) to which ac53a (lef-10) was added later. Partial re-sequencing of the AcMNPV C6 strain at a later date, demonstrated that four ORF pairs were actually fused (ac20/21, ac58/59, ac106/107, ac112/113), bringing the total to 151 ORFs (92). For many ORFs, we had little or no idea about their putative function. Overtime, many ORFs were assigned (see Table 1), mainly associated with transcription, DNA replication, virion structure and pathogenesis. Nevertheless, as of January 2009, 73 ORFs still remain with an unknown function. The most striking ORFs were those involved in the inhibition of apoptosis (p35) and in abrogation of the molt (egt). These observations provoked resonance far beyond baculovirology.
Functional studies in other, closely-related baculovi-ruses are sometimes useful to indicate which role an encoded AcMNPV protein might have. However, discrepancies have been found, which may reflect intrinsic differences in the viral protein under study. The discrepancies may also reflect dissimilarities in the presence or absence of other baculovirus gene products or in the interplay with host factors.
Many of the AcMNPV ORFs with unknown function encode relatively small proteins, sometimes with homologs in only a few baculoviruses, and therefore may not be functional or may not have a very crucial role. Others with unrevealed function, though, belong to the baculovirus core genes at the family level, or are represented in a whole genus, and must play key roles in baculovirus biology. Some of these genes may very well play a role in baculovirus ecology rather than in transcription, gene regulation, DNA replication, or in the assembly of BV and ODV particles. A systematic analysis of knock-out mutants would help in the further functional assignment of AcMNPV ORFs.
Detailed information on the molecular genetics and functional biology of AcMNPV ORFs will contribute to the further development, tailoring and improvement of baculoviruses as biocontrol agents, protein expression vectors and as vectors for gene therapy. This Encyclopedia of AcMNPV genes should be the starting point and further contribute to this venture.
The draft of this manuscript was almost completed when a web-based publication by George F. Rohrmann on "Baculovirus Molecular Biology" was made public.
David Cohen, Bryn Davis and Martin Marek were financed by the project BACULOGENES of the European Union (LSHB-CT-2006-037541). Monique van Oers was sponsored by the Netherlands Scientific Organisation (NWO) MEERVOUD program.
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