The DNA polymerase gene was PCR'ed using specific primers creating an EcoRI cut site at the 5' end of the gene and a Bgl II cut site at the 3' end of the gene. This PCR product was digested with these enzymes and ligated into pUC18 digested with EcoRI and Bam HI. This ligation allows for the production a fusion protein expressed from the Lac promoter replacing the first two amino acids of the native Taq DNA polymerase with the first seven amino acids encoded by the vector. This construct can be induced with IPTG (0.5mM). Although expression is quite leaky in the absence of inducer, expression of the Taq DNA polymerase is not detrimental to growth at 37oC.
Reference:
Desai, U.J. and Pfaffle, P.K. 1995. Single-Step Purification of a Thermostable DNA Polymerase Expressed in Escherichia coli. BioTechniques 19(5):780-784.