Sulfur carrier protein involved in sulfur trafficking in the cell. Part of a sulfur-relay system required for 2-thiolation during synthesis of 2-thiouridine of the modified wobble base 5-methylaminomethyl-2-thiouridine (mnm(5)s(2)U) in tRNA (PubMed:16387657). Interacts with IscS and stimulates its cysteine desulfurase activity (PubMed:16387657, PubMed:23281480). Accepts an activated sulfur from IscS, which is then transferred to TusD, and thus determines the direction of sulfur flow from IscS to 2-thiouridine formation (PubMed:16387657). Also appears to be involved in sulfur transfer for the biosynthesis of molybdopterin (PubMed:23281480). Seems to affect the stability of sigma-S, particularly during the logarithmic growth phase (PubMed:9555915). tRNA modification. Interacts with IscS. Cells lacking this gene are not capable of growing in standard laboratory rich medium (i.e., Luria broth), and show filamentous shape (PubMed:9555915). FtsZ-ring formation appears to be severely impaired in tusA-deficient cells, resulting in the formation of a non-divided filamentous cell (PubMed:10830496). A tusA deletion mutant lacks the 2-thio modification of mnm5s2U in tRNA and has a severe growth defect (PubMed:16387657). Deletion of tusA has a pleiotropic effect on transcription, including increased expression of molybdenum cofactor biosynthesis genes (moaABCDE operon), but leads to reduced activity of molybdoenzymes, an overall low molybdopterin content and an accumulation of the molybdopterin precursor cyclic pyranopterin monophopshate (cPMP) (PubMed:23281480). Belongs to the sulfur carrier protein TusA family.