Amino-acid sequence alignments between the Ssb proteins (gp32s) of T4 and RB69. Residues and segments of the T4 gp32 sequence that have been implicated in specific biological functions of the protein are marked as follows: Db [DNA binding residue]; Zb (residues that coordinate Zn++ in the zinc-binding domain; [20,46]); gp32-gp32 [residues involved in cooperative gp32 binding to ssDNA]; XLgp59 (residue that cross-links to gp59; ); LAST (sequence motifs, (Lys/Arg)3 (Ser/Thr)2, that have been proposed to directly bind nucleic-acids or mediate gp32-gp32 interactions ). The shaded C-terminal portion of T4 gp32 has been implicated in interactions with other phage induced proteins . The small deletion (Δ32PR201) alters specificity of T4 gp32 in phage replication without affecting autogenous translational repression . The largest vertical arrows denote trypsin-hypersensitive sites (19) The G-to-A mutation marked "(ts)" was isolated in this laboratory as a missense (temperature-sensitive) suppressor of a defective gp43 function (unpublished). In the RB69 gp32 sequence, residues whose codons differ from their conserved T4 counterpart at the third nucleotide are underscored with a single dot; those differing by 2 nucleotides are marked by 2 dots.