Has antibacterial activity against a wide variety of haloarchaeons. Causes cell lysis and death, possibly by disrupting the cell wall (PubMed:12811620). Acts as an immunity protein for halocin-C8. Able to block the halocin-C8 activity by sequestering the activity of halocin-C8 through specific and direct binding (PubMed:15978083, PubMed:18658263). Immunity protein HalI interacts with Halocin-C8; the interaction is direct. Secreted (PubMed:15978083, PubMed:12811620). Exclusively localizes to the cell membrane. Increases to maximal levels upon transition from exponential to stationary phase. The helix-loop-helix (HLH) region is essential for immunity function of Immunity protein HalI and interaction with Halocin-C8. Predicted to be exported by the Tat system. The position of the signal peptide cleavage has not been experimentally proven. Is quite robust, as it can be desalted, boiled, subjected to organic solvents, and stored at 4 degrees Celsius for extended periods without losing activity.