The expression product of the cloned aprEin E. coli failed to be detected by general molecular biological methods including SDS-PAGE and protease activity determination. However, the results obtained by microcalorimetric technique showed that there were obvious differences among their metabolism heat-out curves. Further analysis suggested that both up-stream and down-stream regulation sequences of the aprE gene could be the key factor for the expression of this gene in E. coli. Based on the information achieved by the analysis of metabolism heat-out curves, the aprE gene segments were sub-cloned again in another plasmid vector with a stronger promoter, and the gene expression product could be detected by general molecular biological method. The results suggested that microcalorimetric technique be a novel, fast and sensitive method to detect the foreign gene expression and regulation, furthermore to provide some suggestions for genetic engineering.

Key words: Escherichia coli, aprE gene, microcalorimetry, gene expression