Natural LacI from <i>E. coli</i> Yields Faster Response and Higher Level of Expression than the LVA-Tagged LacI

Abstract

The <i>lac</i> promoter is one of the most commonly used promoters for expression control of recombinant genes in <i>E. coli</i>. In the absence of galactosides, the <i>lac</i> promoter is repressed by its repressor protein LacI. Since the <i>lac</i> promoter is regulated by a repressor, overexpression of LacI is necessary for regulation when the promoter is introduced on a high-copy plasmid. For that purpose, a modified variant of LacI, a LVA-tagged LacI, was submitted to the Registry of Standard Biological Parts and has been used for more than 500 constructs since then. We have found, however, that natural LacI is superior to the LVA-tagged LacI as controller of expression