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L. significance of adding the SV40 polyA sequence on gene expression, the expression of the enhanced green fluorescent protein (egfp) was evaluated with and without the presence of SV40 polyA under the control of the polyhedrin promoter at different genomic loci (polyherin, ecdysteroid UDP-glucosyltransferase (egt), and gp37). In this study, spectrofluorometry and western blot showed reduction of EGFP protein for all recombinant viruses with SV40 polyA, whereas qPCR showed an increase in theegfpmRNA levels. Therefore , we conclude that SV40 polyA increases mRNA levels but decreases protein production in the BEVS when the polyhedrin promoter is used at different loci. This work suggests that SV40 polyA in BEVSs should be replaced by an AcMNPV late gene polyA for optimal protein production Auristatin F or left untouched for optimal RNA production (RNA interference applications). == Introduction == The insect specific baculoviruses in the family ofBaculoviridaehave been widely used for high yield expression of heterologous proteins in insect cells for research and pharmaceutical applications [1, 2, 3, 4]. This is attributed to the fact that the large circular dsDNA genome of baculovirus (88180 kb) has genes that are dispensable and can be replaced with foreign genes for expression purposes [5, 6]. For example , in the genome of the most extensively studied baculovirus, Autographa californicamultiple nucleopolyhedrovirus (AcMNPV), the highly expressedpolyhedrin(polh) andp10genes are not essential for AcMNPV replication in cell culture [7, 8]. This discovery leads to the development of the baculovirus expression vector system (BEVS) [7]. The BEVS has at least three major attractive advantages over other systems for gene expression. First, the strong promoters such as those ofpolhandp10allow abundant expression of foreign genes. Second, they support the proper production of the mammalian proteins in insect cell culture or in live insects [9]. Third, the mechanisms LSH for post-translational modification of proteins in insect systems are similar to those in mammalian systems [1, 10]. Two different groups of genes are classified depending on whether they are transcribed prior to or posterior to viral DNA replications . Early genes are transcribed by the host RNA polymerase (POL) II without the need of viral DNA replication. However Auristatin F , the late genes that are transcribed by the viral RNA POL, driven by an early promoter, are transcribed posterior to viral replication [11]. Thepolhpromoter is a strong promoter that drives the expression of a late gene (polyhedrin gene) and has been widely used for protein production in the vast majority of the BEVSs [1, 2]. To further enhance protein production in the BEVS, a 128 bp simian virus 40 (SV40) polyadenylation signal sequence or SV40 polyA has been routinely added to some of thepolhpromoter-based transfer vectors such as the popular Bac-to-BacpFastBacvectors and Gateway-adapted destination vectors (Invitrogen). The SV40 polyA signal is recognized and used by the host RNA POL II complex to process precursor mRNA and increase the stability of the mature mRNA as well as enhance the efficiency of mRNA translation in eukaryotic cells. Therefore , its Auristatin F insertion in the BEVS is intended to provide efficient mRNA processing and polyadenylation and to boost protein expression levels in insect cells. Although critics suggest that additional polyadenylation signals should not be added when foreign genes are to be expressed in the BEVS, the significance of adding polyadenylation signals has not been fully addressed [12]. Early work suggests that the insertion of SV40 polyA at thep10locus in other BEVSs reduces mRNA production and thus reduces protein synthesis [13]. However , the role of SV40 polyA in thepolhpromoter-based vectors has not been systematically investigated. Therefore , we designed different experiments to investigate the influence of using SV40 polyA on enhanced green fluorescent protein (EGFP) expression, which is driven by the polyhedrin promoter in three different loci on the AcMNPV genome. Recording the influence of using SV40 polyA on foreign genes driven by late promoters in BEVS is very important to the baculovirus-based applications such as vaccines, pharmaceutical products Auristatin F and RNA interference. == Materials and Methods == == Cell line and viruses == The insect cell line IPLB-SF21AE (Sf21) used throughout this investigation was maintained at 27C in the TNM-FH medium supplemented with 10% fetal bovine serum. AcMNPV (E2 strain) was used to test the significance of SV40 polyA in the BEVS. The Bac-to-Bacsystem was obtained from Invitrogen. == Recombinant virus construction == Three viral loci were used to test the roles of SV40 polyA in gene expression levels in the BEVS. Transfer vectors were constructed to generate three recombinant viruses that expressegfpin three independent loci (polh, egtandgp37). At thepolhgene locus, for the SV40-construct, a 5. 2 kbpEcoRI/SphI fragment of AcMNPV containingpolhwas cloned between theEcoRI andSphI sites of the pUC18 plasmid. The resultant 7. 9 kbp cloned (pUCpolh) DNA was cleaved withEcoRV/KpnI.