Catalyzes the transfer of an N-acetyl-glucosamine moiety to 1D-myo-inositol 3-phosphate to produce 1D-myo-inositol 2-acetamido-2-deoxy-glucopyranoside 3-phosphate in the mycothiol (MSH) biosynthesis pathway (PubMed:12754249). MSH and WhiB3 are probably part of a regulatory circuit that mediates gene expression upon acid stress (like that found in host macrophage phagosomes) (PubMed:26637353). MSH is one of the major redox buffers which protects bacteria against redox stressors and antibiotics; loss of MSH or ergothioneine (ERG, the other major redox buffer in this bacteria) leads to respiratory alterations and bioenergetic deficiencies that negatively impact virulence (PubMed:26774486). 1D-myo-inositol 3-phosphate + UDP-N-acetyl-alpha-D-glucosamine = 1D-myo-inositol 2-acetamido-2-deoxy-alpha-D-glucopyranoside 3-phosphate + H(+) + UDP Homodimer. Increased intracellular levels of ergothioneine, 8-fold increase in reactive oxygen species-producing cells, decreased resistance to the antibiotics rifampicin, isoniazid, bedaquiline and clofazimine (PubMed:26774486). Increased oxygen consumption and extracellular acidification rates, which are further increased by membrane uncoupler CCCP, indicative of electron chain dysfunction in the absence of MSH (PubMed:26774486). Absence leads to alteration of transcript levels for 139 genes which probably compensate for loss of redox control (PubMed:26774486). Loss of induction of some pH-inducible genes at pH 4.5, including the redox-sensor whiB3 (PubMed:26637353). Belongs to the glycosyltransferase group 1 family. MshA subfamily.