Prokaryotic expression, purification, and production of polyclonal antibody against novel human serum inhibited related protein I (SI1).

A novel serum inhibited related gene (SI1) has been cloned in our lab by using mRNA differential display analysis of U251 cells in the presence or absence of serum, the expression of SI1 was dramatically inhibited by the addition of serum to serum starved cells. Previous reports suggested the potential significance of SI1 in regulating the cell cycle. In this study, the plasmid construction, protein expression and purification, as well as the generation of anti-SI1 polyclonal antibody are described. A full-length cDNA of Si1 was inserted in a prokaryotic expression plasmid pET28-b(+) and efficiently expressed in E. coli Rosetta (DE3) strain after induction by isopropyl-b-D: -thiogalactoside. The expressed 6His-tagged SI1 fusion protein was purified by Ni(+) affinity column and then used to immunize Balb/C mice, and the anti-SI1 polyclonal antibody was purified by protein A column. To determine the sensitivity and specificity of the antibody against SI1, a cell lysate of pEGFP-N2-SI1 plasmid transiently transfected Hela cell was identified by anti-GFP monoclonal antibody and anti-SI1 polyclonal antibody. Both the GFP-SI1 fusion protein and endogenous SI1 protein in Hela cell can be recognized by the anti-SI1 polyclonal antibody. The anti-SI1 polyclonal antibody will provide a useful tool for further characterization of SI1.