The carboxy-terminal region of translational initiation factor IF2 is a common region to the three active forms of the factor (α,β and γ) 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 lambda represser, e.g. the helix-tum-helix motif and some of the residues essential for the structure of the hydrophobic core of the represser. This homologous domain of IF2 was fused to the β-galactosidase protein. The hybrid protein, as well as IF2 itself, shows a consistent DNA binding activity in nitrocellulose filtration assays but does not display the specificity of the cI represser for the Pr operator. The implication of this domain in the transcriptional activity of IF2, reported by others, is discussed.
