Toxic component of a type I toxin-antitoxin (TA) system (PubMed:20156992, PubMed:24203704, PubMed:27903909, PubMed:31277504). Expression in the absence of its cognate antitoxin (small sRNA orzO) leads to cell stasis and a decrease in colony-forming units (PubMed:24203704, PubMed:27903909). Repression of ZorO toxicity requires base pairing between zorO mRNA and sRNA OrzO, as well as RNase III (rnc), suggesting the mRNA is degraded. Base pairing occurs between 18 bases in the 5' UTR of zorO mRNA and the 5' end of OrzO sRNA. sRNA OrzP, which differs only in 4 of these 18 bases, does not repress ZorO toxicity (PubMed:24203704). Integration of the protein into the inner membrane damages membrane integrity and affects membrane potential. It leads to increased levels of hydroxyl radicals (PubMed:31277504). Expressed during exponential growth in rich medium and at lower levels in exponential and stationary phase in minimal medium (zorO mRNA cannot be distinguished from zorP mRNA by these assays as they are practically identical) (PubMed:20156992). Translation of this mRNA is repressed by secondary structures in its 5' UTR and partially by OrzO sRNA. Processing of the 5' UTR increases its translation in vitro and comparative toxicity in vivo (PubMed:27903909). A short internal peptide (AARL, residues 20-24) is toxic against B.subtilis, S.aureus and the yeast Candida albicans but not against E.coli, green monkey (Vero) or hamster cells (BHK) cultured cells. It functions in various growth media and might be used as an antimicrobial peptide. The intact protein is not toxic under any tested conditions when added to growth medium.