Publisher Summary Halocin activity is usually confined to other haloarchaea, with some inhibiting many species (a broad spectrum) and others just a few (a narrow spectrum) However, halocins A4, R1 and S8, all inhibit three species of Sulfolobus (a hyperthermophilic crenarchaeote), with halocin R1 also inhibiting Methanosarcina thermophila. Halocin pre-proteins (e.g. halocin H4) or preproproteins (e.g. halocin S8) are secreted using the twin-arginine translocation (Tat) pathway. This is the preferred pathway for translocating proteins in the haloarchaea. Halocin H1 activity first appears during mid-exponential phase, halocin H4 activity first appears and spikes during the transition into stationary phase, but then declines rapidly from peak levels, and halocin R1 appears relatively late in stationary phase. The general considerations while purifying halocins are, Halocin activity should be quantified at each step of the purification in order to follow the progress of the purification and to determine the loss of halocin activity along the way. Samples should be set aside at each step of the purification and assayed by SDS-PAGE in order to visualize the purity of the halocin at the final step.