Enhances recognition of ssrA-tagged proteins by the ClpX-ClpP protease; the ssrA degradation tag (AANDENYALAA) is added trans-translationally to proteins that are stalled on the ribosome, freeing the ribosome and targeting stalled peptides for degradation. SspB activates the ATPase activity of ClpX. Seems to act in concert with SspA in the regulation of several proteins during exponential and stationary-phase growth. Also stimulates degradation of the N-terminus of RseA (residues 1-108, alone or in complex with sigma-E) by ClpX-ClpP in a non-ssrA-mediated fashion. Homodimer. Binds 1 ssrA-tag per monomer; if the first Asn residue of the ssrA tag is mutated to Ala, SspB no longer binds the protein or stimulates ClpX-ClpP degradation (PubMed:11009422). Binds the N-terminus (residues 1-108) of RseA with and without sigma-E (PubMed:15371343); although ssrA and the N-terminal fragment of RseA both bind to SspB competitively they bind in opposite directions in its peptide-binding groove. By amino acid starvation. Decreased degradation of ssrA-tagged proteins by ClpX-ClpP, no effect on degradation by ClpA-ClpP protease. Delayed and decreased induction of the extracytoplasmic-stress response. Belongs to the SspB family.