Analysis of low temperature inducible mechanism of gamma-glutamyltranspeptidase of Escherichia coli K-12.

Escherichia coli K-12 cultured at 20 degrees C has more gamma-glutamyltranspeptidase (GGT: EC 2.3.2.2) activity than that cultured at 37 or 42 degrees C. On Western blot analysis, E. coli K-12 cells cultured at 20 degrees C produced more GGT protein than those cultured at 37 degrees C. mRNA of the GGT gene (ggt) in the cells was also measured and it was found that the level of ggt mRNA at 20 degrees C was 10-fold higher than that at 37 degrees C. When the ggt promoter was replaced by a tac promoter, GGT activity at 37 degrees C from the tac promoter was 5-fold higher than that at 37 degrees C from the ggt promoter, though there was less difference in GGT activity between both grown at 20 degrees C. The ggt mRNA at 20 degrees C was found to be more stable than that at 37 degrees C. These results suggested that the higher GGT activity in E. coli K-12 cells grown at 20 degrees C was due to a higher level of GGT protein at 20 degrees C caused by higher level of ggt mRNA at 20 degrees C because of a low-temperature dependent ggt promoter as well as the stability of ggt mRNA at 20 degrees C.