Binds to H-NS and modifies the range of genes it silences; H-NS alone silences 'core' genes while the H-NS-Hha complex (and presumably also H-NS-YdgT) silences genes acquired by horizontal gene transfer (PubMed:19521501). Plays a role silencing virulence factors in the absence of factors that induce pathogenicity (PubMed:17307861). Probably requires H-NS to bind DNA (By similarity). Interacts with H-NS (By similarity). Derepression of pathogenicity island 2 (SPI-2) which is usually repressed in culture; effect is slightly higher in double hha-ydgT deletions (PubMed:17307861). Double hha-ydgT deletion mutants lead to deregulation of many genes at least 2-fold, most of which are also deregulated in an hns deletion, suggesting there are a large number of hns-regulated genes whose expression is also modulated by Hha and/or YdgT (PubMed:19521501). Upon infection of C57BL/6 mice a single hha mutant has 10-100-fold reduced virulence compared to wild-type, while a double hha-ydgT deletion is 6 orders of magnitude less virulent (PubMed:17307861). Belongs to the Hha/YmoA/Cnu family.