Functions as a sulfur delivery protein for Fe-S cluster synthesis onto IscU, an Fe-S scaffold assembly protein, as well as other S acceptor proteins. Catalyzes the removal of elemental sulfur atoms from cysteine to produce alanine. [sulfur carrier]-H + L-cysteine = [sulfur carrier]-SH + L-alanine Optimum pH is 8.3-8.6. Optimum temperature is 37 degrees Celsius. Cofactor biosynthesis; iron-sulfur cluster biosynthesis. Homodimer. Forms a heterotetramer with IscU, interacts with other sulfur acceptors. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. NifS/IscS subfamily.