Seminal plasmin, an antimicrobial protein from bull semen, inhibits gene expression in E. coli

RNA synthesis in Escherichia coli was immediately inhibited after addition of seminal plasmin, an antimicrobial protein from bull semen. RNA synthesis progressively decreased within 12 min and then ceased completely. In contrast, protein synthesis was not affected within the first 12 min, but thereafter became progressively inhibited. Inhibition of RNA synthesis by seminal plasmin in E. coli interfered with induction of beta-galactosidase by isopropyl-beta-D-thiogalactoside (IPTG). This implied inhibition of beta-galactosidase mRNA synthesis by seminal plasmin in vivo. The sensitivities of total in vivo RNA synthesis and beta-galactosidase mRNA synthesis against seminal plasmin were found to be similar. Seminal plasmin had no effect on the uptake of the inducer IPTG by E. coli cells.