Expression of cho and melC operons by a Streptococcus thermophilus synthetic promoter in Escherichia coli

A 63-base-pair synthetic promoter, sP1, was synthesized on the basis of the nucleotide sequence of a putative Streptococcus thermophilus promoter. When inserted upstream from the Streptomyces cho operon in a recombinant plasmid, pUCO19SP-36, sP1 activated the expression of the cho genes in Escherichia coli, as shown by the production of cholesterol oxidase by the transformants. The sP1-driven cholesterol oxidase production in pUCO195P-36-transformed cells was estimated to be 40% of that produced by Plac-mediated cho expression in a pUCO193-containing host. The recombinant pUCO195P-36 appeared to be segregationally less stable in E. coli DH5 alpha than in HB101. Its nonexpressing counterpart, pUCO195P-1, was stable in both E. coli strains. The activity of sP1 was further demonstrated in E. coli by the expression of a Streptomyces melC operon. When placed upstream from the test operon in the pMCU22aPa construct. sP1 activated the melC expression as shown by the production of tyrosinase at (3.0+/-0.3)X 10(-3) U/mg and (16.0+/-1.0)X10(-3)U/mg protein equivalent of cell extract in the absence and presence of isopropyl beta-D-thiogalactopyranoside, respectively. The presence of a counter-oriented Plac at the 3' end of the operon in the pMCU22bPa plasmid reduced the sP1-mediated tyrosinase production by about 85%.