New 434-Specific DNA Binding Protein Copurified with the 434 tof Protein from λimm⁴³⁴cI dv Carrier Cells of Escherichia coli

Abstract

A tof-like protein that has 434-specific DNA binding activity has been copurified with the 434 tof protein from λimm⁴³⁴cl dv carrier cells. The apparent molecular weight of the new 434-specific DNA binding protein is 9, 000 to 9, 500, a little higher than that of the 434 tof protein, as estimated by SDS gel electrophoresis. Amino acid analysis revealed the protein to be an arginine-rich component whereas the 434 tof protein is a lysine-rich component. The specific binding reaction of the new protein to λimm⁴³⁴ dv DNA is distinct from that of the 434 tof protein in respect to the sigmoid shape of the binding curve and to the temperature dependency. This suggests that the specific binding to λimm⁴³⁴ dv DNA observed with the new protein is due not to a trace of the 434 tof protein contaminating the new protein preparation but rather to the new protein itself. The NH₂-terminal 11 residues of the new 434-specific DNA binding protein were sequenced by manual Edman degradation. This technique revealed that the new protein is not a fragment of the 434 tof, cll, or O protein or an NH₂-terminal fragment of the cl repressor. The origin and the physiological roles of the new 434-specific DNA binding protein remain unknown.