Single-strand DNA-binding protein (SSB) is a protein found in Escherichia coli (E. coli) bacteria, that binds to single-stranded regions of deoxyribonucleic acid (DNA).

Active E. coli SSB is composed of four identical 19 kDa subunits.

Binding of single-stranded DNA to the tetramer can occur in different "modes", with SSB occupying different numbers of DNA bases depending on a number of factors, including salt concentration.

Further work is required to elucidate the functions of the various binding modes in vivo.

[2] It has a structure of three beta-strands to a single six-stranded beta-sheet to form a protein dimer.