Down-regulates hemolysin (hly) expression in complex with H-NS (PubMed:1956303, PubMed:10778755, PubMed:11790731, PubMed:21600204). Stimulates transposition events in vivo (PubMed:8145648). Modifies the set of genes regulated by H-NS; Hha and Cnu (YdgT) increase the number of genes DNA bound by H-NS/StpA and may also modulate the oligomerization of the H-NS/StpA-complex (PubMed:23543115). Binds DNA and influences DNA topology in response to environmental stimuli; does not however interact with DNA in the absence of H-NS (PubMed:23543115). Involved in persister cell formation, acting downstream of mRNA interferase (toxin) MqsR (PubMed:19909729). Decreases biofilm formation by repressing the transcription of fimbrial genes fimA and ihfA, and by repressing the transcription of tRNAs corresponding to rare codons, which are abundant in type 1 fimbrial genes (PubMed:18545668). Forms a heterotrimeric complex with the H-NS dimer in the absence of DNA. Expression is autoregulated (Probable). Induced during biofilm formation (PubMed:14727089, PubMed:18545668). Histidine-tagging (His-tagging) at the N-terminus does not impair interaction with H-NS, whereas His-tagging at the C-terminus does impair interaction (PubMed:11790731). Deletion results in a large increase in the production of extracellular and intracellular hemolysin (PubMed:1956303). At low osmolarity minor changes in overall translation, at 0.4 M NaCl expression of about 25 proteins altered, including decreased OmpA, crr and AhpC (in strain 5K, not a K12 derivative) (PubMed:10322001). At 0.3 M NaCl in strain W3110 up-regulation of 113 genes and down-regulation of 8 genes was observed; a double cnu-hha deletion up-regulated 134 and down-regulated 5 genes, most of which are thought to have been acquired horizontally and are also up-regulated in double hns-stpA deletions (PubMed:23543115). However there are only 12 genes that were commonly up-regulated in the hha and cnu-hha deletions (PubMed:23543115). Represses the production of persister cells (PubMed:19909729). Deletion of hha and tomB (ybaJ), in the presence of a conjugative plasmid (R1drd19), decreases biofilm formation, cell aggregation and increases motility via flagella and motility gene expression (PubMed:16317765). Hha and TomB may form a type II toxin-antitoxin (TA) system (PubMed:18545668). Belongs to the Hha/YmoA/Cnu family. Extended N-terminus.