The heme-regulated inhibitor was originally identified as the translation-level regulator that couples ��-globin synthesis with heme levels during erythropoiesis and has more recently been shown to mitigate oxidative stress during erythroid differentiation. HRI is also important for various stress responses in yeast and mammalian cells. Here we investigated whether HRI plays a role in host cell infection by microbial pathogens. Unexpectedly, we found that HRI positively regulates specific virulence-related activities of diverse bacterial pathogens. Surprisingly, these HRI effects were independent of its canonical function as a translation regulator via eIF2�� and thus identify a novel role for HRI in bacterial pathogenesis. Here we demonstrate that HRI positively affects the cell-level infection dynamics of three dissimilar bacterial pathogens. The extracellular pathogen Yersinia, the vacuole-bound pathogen Chlamydia, and the cytosolic pathogen Listeria, all require HRI to efficiently complete their respective cellular infection cycles. A common denominator among these three pathogens is that they all require access to the infected cell cytosol: either for their virulence factors to manipulate host cell processes or for the bacterium itself to reach the compartment in which it proliferates. How could a HRI-mediated Bepridil hydrochloride process promote pathogen access to the host cytosol? A commonality among the three pathogens used in our studies is that their respective infection cycles are dependent on forming pores in infected host cellular membranes. In Gram-negative pathogens such as Yersinia and Chlamydia, the T3S secrete translocators that assemble poreforming structures in the host plasma membrane that mediate the transfer of effectors into the cytosol. In some respects this process resembles that which occurs in Listeriainfected cells. Following its invasion of the host cell, Listeria secretes monomeric LLO that, following its activation by the host-encoded gamma-interferon-inducible lysosomal thiol reductase, binds to and oligomerizes into poreforming structures within the endosomal membrane. In addition to allowing leakage of antimicrobial factors, the resulting pores are also thought to allow the access of co-expressed and secreted phospholipases to the inner leaflet of the endosomal membrane. It is possible that one or more of these events occur with reduced efficiency in HRI null cells. We believe that the activities of HRI described here neither AZ 10606120 dihydrochloride involve it acting as an eIF2�� kinase nor otherwise affecting protein synthesis. That T3S secretion is not coupled to host cell protein translation was indicated by our finding that cycloheximide treatment did not affect YopE-mediated disruption of the host cell cytoskeleton.