Toxic component of a type II toxin-antitoxin (TA) system. A sequence-specific endoribonuclease, cleavage occurs after the first AU in the consensus sequence AUA(U/A); RNA secondary structure is probably important in substrate choice. Cuts in 5' and 3' UTRs. The TA system acts as a post-transcriptional regulator of carbon metabolism; in M.smegmatis 3 TA systems (VapB-VapC, MazE-MazF and Phd-Doc) may be involved in monitoring the nutritional supply and physiological state of the cell, linking catabolic with anabolic reactions. When overexpressed inhibits cell growth, via translation; 10-fold in a wild-type strain, 100-fold in a vapB-vapC disruption mutant (PubMed:19445953). Overexpression of VapC leads to differential expression of 205 genes; many down-regulated genes are predicted to be involved in the transport and catabolism of carbohydrates, while genes involved in phosphate transport and scavenging are up-regulated. VapC is bacteriostatic, not bacteriocidal; cells are ovoid, non-replicating and have decreased transcription, becoming dormant (PubMed:24417293). Digests ssRNA but not tRNA, dsRNA, ssDNA or dsDNA. The VapB-VapC complex binds its own promoter DNA, and VapC alone binds RNA. Forms a complex with VapB. Expression is low but constitutive, and repressed by VapB-VapC. Translation of vapC mRNA requires VapB. Member of the vapB-vapC operon. The vapB-vapC operon is not essential; cells grow faster than wild-type on rich and minimal glycerol-containing medium. The operon deletion mutants die faster than wild-type under potassium-limiting conditions, which is prevented by overexpression of vapB (PubMed:24417293). The vapB antitoxin gene can be disrupted without causing death, however despite elevated vapC transcription, no VapC protein could be detected, suggesting that RNA processing and translational coupling are important in VapC expression. A triple TA mutant (missing vapB-vapC, mazE-mazF and phd-doc TA systems) survives antibiotic challenge, suggesting the TA systems are not required to generate drug-resistant cells. However the triple mutant is more sensitive to oxidative and heat stress, and does not survive long-term starvation during aerobic growth on complex medium. There is a difference in the level of branched-chain amino acids, which may play a role in monitoring the nutritional supply and physiological state of the cell. Belongs to the PINc/VapC protein family.