During stationary phase, promotes and stabilizes dimerization of 70S ribosomes by the ribosome modulation factor (RMF), leading to the formation of inactive 100S ribosomes (PubMed:18174192). Converts immature 90S particles formed by RMF into 100S ribosomes (PubMed:16324148). Crystallization with T.thermophilus 70S ribosomes shows it binds in the channel between the head and body of the 30S subunit, where mRNA, tRNAs, initiation factors IF1 and IF3 and elongation factor G would bind; however RMF is still able to bind (PubMed:22605777). In this crystal binding of HPF induces movement of the 30S head domain away from the rest of the ribosome, presumably so they would more easily form dimers (PubMed:22605777). May also function as a potential translational inhibitor (PubMed:18174192). Associates exclusively with 100S ribosomes, which are dimers of 70S ribosomes. Induced during stationary growth phase (at protein level) (PubMed:11168583). Induced by the signal autoinducer AI-2 (PubMed:11514505). Non-essential gene, no formation of inactive 100S ribosomes. Double hpf-yfiA deletion mutants form 90S ribosomes (PubMed:16324148). A quadruple yfiA-hpf-rmf-sra knockout strain is significantly outcompeted by wild-type after 4 days growth (PubMed:17277072). No change in sensitivity to aminoglycoside antiobiotic gentamicin in stationary phase cultures (PubMed:26324267). Belongs to the HPF/YfiA ribosome-associated protein family. Short HPF subfamily.