Transfection of mouse cells with thymidine kinase gene of herpes simplex virus

A simple procedure for expression and purification of selected non-structural (alpha and beta) herpes simplex virus 1 (HSV-1) proteins

The expression and isolation of herpes simplex virus 1 (HSV-1) immediate early (alpha) IE63 (ICP27) and of the early (beta) thymidine kinase (Tk) polypeptides in Escherichia coli JM 109 cells transformed with the PinPoint Xa-1 (Promega) plasmid construct carrying either the HSV-1 UL54 or UL23 genes are described. The resulting biotinylated fusion protein(s) could be easily induced and were purified in appropriate amounts by means of a monomeric avidin-conjugated resin (SoftLink Soft Release Avidin Resin, Promega) provided that: (1) the exponential growth of the selected transformed cells was monitored carefully; (2) the post-induction harvest interval was properly chosen; and (3) the period for adsorption to the avidin resin suitably adjusted. The isolated protein(s), although partially digested in the case of the IE63 polypeptide, were suitable antigen(s) for immunization of various animal species. Co-purification of trace amounts of endogenous biotinylated protein(s) produced in E. coli was eliminated by shortening the duration of adsorption to the avidin resin.

Differential intracellular compartmentalization of herpetic thymidine kinases (TKs) in TK gene-transfected tumor cells: molecular characterization of the nuclear localization signal of herpes simplex virus type 1 TK

The thymidine kinases (TKs) of herpes simplex virus type 1 (HSV-1), HSV-2, and varicella-zoster virus (VZV) were expressed in human osteosarcoma cells as fusion proteins with the green fluorescent protein (GFP), and their intracellular localizations were determined. The three TK-GFP fusion products were localized in different subcellular compartments of the transfected tumor cells. HSV-1 TK-GFP was localized exclusively in the nucleus, HSV-2 TK-GFP was predominantly found in the cytosol, while VZV TK-GFP was localized in both the nucleus and the cytosol. In support of these findings, we identified a nuclear localization signal (NLS) in the N-terminal arginine-rich region of HSV-1 TK that was absent in HSV-2 and VZV TK. The first 34 amino acids proved necessary for the specific nuclear localization of HSV-1 TK and, when added to the VZV TK-GFP gene construct, also sufficed to specifically target VZV TK-GFP to the nucleus. Further analysis of this NLS through site-directed mutagenesis revealed that the basic amino acid-rich nonapeptide 25R-R-T-A-L-R-P-R-R33 is of crucial importance in the nuclear targeting of HSV-1 TK. In particular, we revealed that the presence of the arginine residues at positions 25, 26, 30, 32, and 33 is obligatory for efficient NLS functioning, whereas arginine and histidine residues outside of the nonapeptide (i.e., residues R18, R20, and H22) did not change the functional properties of the NLS.