Mutational Analysis of the Role of vir-box in the Expression of the virE Gene

To elucidate the role of vir-box in the expression of the virE gene, the vir-box was modified by site-directed mutagenesis and tested for β-galactosidase activities. A, C, T → T, A, C substitutions at -62, -63 and -65 positions, destroying the 5'-region of the vir-box and A→ T at position -55, destroying the S'-region of the vir-box respectively, showed only 17% promoter activity. When the vir-box was modified to contain perfect dyad symmetry structure (DSR) by the substitutions T, G → A, T at - 60 and - 61 positions, β-galactosidase activity increased 302%. These results indicate that the 5' and 3'-region of vir-box as well as the imperfect DSR of the vir-box itself may play a very important role in the regulation of virE gene expression.