The function of Ensembl gene identifier ENSG00000124217 (MOCS3, molybdenum cofactor synthesis 3) is as follows. Plays a central role in 2-thiolation of mcm(5)S(2)U at tRNA wobble positions of cytosolic tRNA(Lys), tRNA(Glu) and tRNA(Gln) (PubMed:19017811, PubMed:22453920, PubMed:30817134). Also essential during biosynthesis of the molybdenum cofactor (PubMed:15073332, PubMed:22453920, PubMed:30817134). Acts by mediating the C-terminal thiocarboxylation of sulfur carriers URM1 and MOCS2A (PubMed:15073332, PubMed:19017811, PubMed:22453920). Its N-terminus first activates URM1 and MOCS2A as acyl-adenylates (-COAMP), then the persulfide sulfur on the catalytic cysteine is transferred to URM1 and MOCS2A to form thiocarboxylation (-COSH) of their C-terminus (PubMed:19017811, PubMed:22453920). The reaction probably involves hydrogen sulfide that is generated from the persulfide intermediate and that acts as a nucleophile towards URM1 and MOCS2A (PubMed:15073332, PubMed:22453920). Subsequently, a transient disulfide bond is formed (PubMed:15073332, PubMed:22453920). Does not use thiosulfate as sulfur donor; NFS1 acting as a sulfur donor for thiocarboxylation reactions (PubMed:18650437, PubMed:22453920). {ECO:0000255|HAMAP-Rule:MF_03049, ECO:0000269|PubMed:15073332, ECO:0000269|PubMed:18650437, ECO:0000269|PubMed:19017811, ECO:0000269|PubMed:22453920, ECO:0000269|PubMed:30817134}.