High-level expression of porcine muscle adenylate kinase in Escherichia coli: effects of the copy number of the gene and the translational initiation signals.

Porcine muscle adenylate kinase (ADK) was overproduced in Escherichia coli using the expression plasmid with double A-T-G codon at the translational starting site and the Shine-Dalgarno (SD) sequence 10 bp apart from the first A-T-G. We used the expression vectors pKK223-3 and pMK2. pMK2 is about 10-20 times larger in copy number than pK223-3. For both vectors, duplication of A-T-G was effective and the quantity of the expressed ADK from the double A-T-G plasmid was 2 approximately 4-fold more than that achieved when only one A-T-G was present. The amount of the produced ADK was maximum in the case of using pMK2 with double A-T-G. The overproduced ADK formed inclusion bodies in E. coli. It was solubilized in 6 M guanidine hydrochloride and refolded. Through two steps of column chromatography, ADK was purified. It has the same amino acid composition and grossly the same activity as that reported by Schirmer et al. (1970). Its amino acid sequence of the NH2-terminal region was identical with that deduced from the cDNA sequence including the NH2-terminal methionine.