DOMAIN OF ESCHERICHIA-COLI TRANSLATIONAL INITIATION FACTOR-IF2 HOMOLOGOUS TO LAMBDA CI REPRESSOR AND DISPLAYING DNA-BINDING ACTIVITY

The carboxy-terminal region of translational initiation factor IF2 is a common region to the three active forms of the factor (alpha, beta a nd gamma) but its function is still unknown. We report here that this region of IF2 carries at least one domain which is homologous to the N -terminal and middle part of the cI repressor of lambda phage. The IF2 homologous domain harbors functionally important features of the lamb da repressor, e.g. the helix-turn-helix motif and some of the residues essential for the structure of the hydrophobic core of the repressor. This homologous domain of IF2 was fused to the beta-galactosidase pro tein. The hybrid protein, as well as IF2 itself, shows a consistent DN A binding activity in nitrocellulose filtration assays but does not di splay the specificity of the cI repressor for the P(R) operator. The i mplication of this domain in the transcriptional activity of IF2, repo rted by others, is discussed.