A novel way to purify recombinant baculoviruses by using bacmid. Biosci Rep. 2009;29:71-75. [PMID: 18684105 DOI: 10.1042/BSR20080074]

A selection marker-free method for gene deletion and editing in baculovirus genomes

Here, we develop a simple, efficient, bacmid-based, selection marker-free method for gene deletion and editing in baculovirus genomes. Specifically, based on pFastbac1, a donor plasmid with long left and right homology arms but without a reporter was constructed for disrupting ie1, an essential baculovirus gene. Instead of ligating with a plasmid, the homology arms were introduced to the polyhedrin locus of BmNPV bacmid using the BmNPV bac-to-bac expression system. Two viruses generated from the modified bacmid and unmodified BmNPV bacmid were then used to co-infect BmN cells in order that recombination takes place at the ie1 locus between them. Finally, without multiple rounds of purification, total cellular DNA was isolated, transformed into Cacl₂-treated competent DH10B cells, and then blue colonies were selected for PCR screening. Remarkably, the proportion of blue colonies containing ie1-disrupted bacmid was found to be around 7 %. Moreover, using primers flanking the homology arms further confirmed that all these positive recombinants were double crossovers. These findings indicate that our method is also capable of gene modification if inverse PCR or seamless cloning is used to construct the donor plasmid and sequencing is employed to select positive colonies.

Expression of Helicobacter pylori γ-glutamyltransferase in silkworm cells using a baculovirus expression system

AIM: To express the Helicobacter pylori (H. pylori) γ-glutamyltransferase (GGT) in silkworm cells using a baculovirus expression system and analyze its activity in vitro.

METHODS: The structure characteristics of the H. pylori ggt gene was analyzed using biological informatics software. The genomic DNA of H. pylori was extracted and used as template to amplify the ggt genes encoding proteins with and without signal peptide by polymerase chain reaction (PCR). After sequencing, the amplified ggt gene encoding protein without signal peptide was fused with a green fluorescent protein (GFP) sequence. Subsequently, the two amplicons and the fusion sequence were cloned into the baculovirus transfer vector pFastBac1, respectively. Bac-to-Bac baculovirus system was then used to generate recombinant virus DNA. Recombinant virus DNA was transfected into silkworm BmN cells to obtain recombinant viruses. The viruses were harvested and used to infect BmN cells again. After infection, BmN cells were harvested to detect protein expression and enzymatic activity. Fluorescence was observed in infected cells using a fluorescence microscope.

RESULTS: The ggt genes encoding proteins with and without signal peptide were successfully cloned by PCR. Sequencing results indicated that no mutations occurred. All the three recombinant viruses obtained could express GGT. The activity of GGT expressed by the recombinant viruses harboring the ggt genes encoding proteins with and without signal peptide and the fusion sequence was 3.61, 10.50 and 9.31 U/L, respectively. Western blot assay demonstrated the expression of GGT-GFP fusion protein. Fluorescent microscopy showed that the fluorescence was distributed throughout the whole cell, indicating that GGT expression is not confined to a certain organelle.

CONCLUSION: GGT with enzymatic activity can be expressed in silkworm cells using the baculovirus expression system.