The function of LIAS (lipoic acid synthetase, Ensembl gene identifier ENSG00000121897) is as follows. Catalyzes the radical-mediated insertion of two sulfur atoms into the C-6 and C-8 positions of the octanoyl moiety bound to the lipoyl domains of lipoate-dependent enzymes, thereby converting the octanoylated domains into lipoylated derivatives. {ECO:0000255|HAMAP- Rule:MF_03123}.