om the hrs is found and called the non-hr, which can also serve as an origin of DNA replication (134, 138). The non-hr region is also associated with the formation of "defective interfering particles" (DIs), which are generated as an artifact in cell culture and which interfere with the replication and production of infectious BVs (145, 222). These DI particles are baculoviruses with reduced size and genome content and a higher frequency of non-hr sequences. DIs are unable to propagate autonomously.
The purpose of this review is to provide an overview of the current knowledge on the function of AcMNPV ORFs and to serve as a starting point for researchers and students to gather further detailed information on particular ORFs. The overview will also assist researchers working with other baculoviruses, which carry homologous genes. In this review, all ORFs are listed in their order of appearance in the AcMNPV genome beginning wit the ptp gene (5'-3') and named according to the GenBank file (NC_ 001623). We choose for an encyclopaedic layout in which a short description of each ORF is presented, together with a small number of selected literature references referring to key publications, and/or review papers through which further relevant literature may be found. In the current paper the description of each ORF starts with the ORF number, e.g. ac1, where ac stands for AcMNPV and "1" for the number of the ORF as indicated in the database. This ORF number is followed by the name of the gene and by the name of the gene product. A genomic map of AcMNPV is given in Fig. 1, which serves to visualize the direction of transcription for individual ORFs and their genetic environment. The indicated sizes are the predicted molecular masses and the length in amino acids (aa) for the primary translation products. Post translational modifications can of course affect the actual size of the protein. A summary of the data is presented in Table 1. In this table the ORFs are also functionally categorized into four groups: genes for virion structure, DNA replication, transcription and auxiliary functions. Auxiliary genes are those that are not necessary for virus replication but give replication advantages for the virus at the level of the cell, the organism or the ecosystem (197).
In Table 2 and Table 3, AcMNPV gene orthologs are indicated for the 48 baculoviruses that have been completely sequenced (December 2008). The numbers correspond to their respective ORF number in the particular virus. Homologous genes have been found using Basic Local Alignment Tool (6) for proteins available through the website http://blast.ncbi.nlm.nih.gov/ with the following search set: non-redundant protein sequence database; organism: dsDNA viruses, no RNA stage; blast-p algorithm. Baculoviruses have a common set of 30 genes and these genes are designated as the baculovirus core genes (178, 179). Two Ac-MNPV genes have homologs in all baculoviruses except for the Deltabaculoviruses (ac25 and ac145), one AcMNPV gene has a homolog in all, except Gammabaculoviruses (ac23), twenty in all Alpha-and Betabaculoviruses and sixteen additional genes have homologs in all sequenced Alphabaculoviruses (Table 2 and Table 3).
Ac1: ptp/bvp, protein tyrosine phosphatase or baculovirus phosphatase
This ORF encodes a protein (19.3 kDa; 168 aa) with a chimerical character as it has the characteristics of a protein tyrosine phosphatase (PTP), but it also has RNA-tri/diphosphatase activity (255). The preferred substrate for PTP is RNA and it crystallizes in a metazoan RNA capping enzyme fashion (27). Later it was renamed to baculovirus phosphatase (BVP), which is a protein only produced by group Ⅰ NPVs. The AcMNPV ptp/bvp gene appears to be associated with the wandering behaviour of infected larvae (107), similarly to the closely related Bombyx mori (Bm) NPV ptp gene (122). RNA-triphosphatase activity is also encoded by the AcMNPV lef-4 gene (ac90), which in addition encodes guanyltransferase activity (154).
Ac2: bro, baculovirus repeated ORF
This gene belongs to the baculovirus repea