Autographa californica multiple nucleopolyhedrovirus me53 (ac140) is a non-essential gene required for efficient budded virus production.
De Jong, J.D., Arif, B.M., Theilmann, D.A., and Krell, P.J. (2009). "Autographa californica multiple nucleopolyhedrovirus me53 (ac140) is a non-essential gene required for efficient budded virus production.", Journal of Virology, 83(15), pp. 7440-7448. doi : 10.1128/JVI.02390-08
Me53 is a highly conserved baculovirus gene found in all lepidopteran baculoviruses that have been fully sequenced to date. The putative ME53 protein contains a zinc finger domain and has been previously described as a major early transcript. We generated a me53-null bacmid (AcDeltame53GFP) as well as a repair virus (AcRepME53:HA-GFP) carrying me53 with a C-terminal HA tag, under the control of its native early and late promoter elements. Sf-9 and BTI-Tn-5b1 cells transfected with AcDeltame53GFP resulted in a 3 log reduction in budded virus (BV) production compared to both the parental AcMNPV and repair bacmids, demonstrating that although me53 is not essential for replication, replication is compromised in its absence. Our data also suggests that me53 does not affect DNA replication. Cell fractionation showed that ME53 is found in both the nucleus and cytoplasm as early as 6 h pi Deletion of the early transcriptional start site resulted in a 10 to 360 fold reduction of BV yield, however deletion of the late promoter (ATAAG) resulted in a 160 to 1,000 fold reduction, suggesting that, in the context of BV production, ME53 is required both early and late in the infection cycle. Additional Western blot analysis of purified virions from the repair virus revealed that ME53:HA is associated with both BV and occlusion derived virions (ODV). Together these results indicate that me53, though not essential for viral replication, is required for efficient BV production.