Catalyzes the removal of elemental sulfur from cysteine to produce alanine (By similarity). Seems to be required for NAD biosynthesis (PubMed:8444804). [sulfur carrier]-H + L-cysteine = [sulfur carrier]-SH + L-alanine Repressed in the presence of nicotinic acid. Cells lacking this gene require nicotinic acid for growth. Belongs to the class-V pyridoxal-phosphate-dependent aminotransferase family. NifS/IscS subfamily.