Stimulates the cysteine desulfurase activity of CsdA. Contains a cysteine residue (Cys-61) that acts to accept sulfur liberated via the desulfurase activity of CsdA. May be able to transfer sulfur to TcdA/CsdL. Seems to support the function of TcdA in the generation of cyclic threonylcarbamoyladenosine at position 37 (ct(6)A37) in tRNAs that read codons beginning with adenine. Does not appear to participate in Fe/S biogenesis