Two mitochondrial ribosomal proteins, YmL13 and MRP7, of the yeast Saccharomyces cerevisiae and their derivatives were synthesized in vitro and their transport into isolated yeast mitochondria was examined. Both proteins were transported into yeast mitochondria in an energy-dependent manner. MRP7 protein was transported even when its N-terminal presequence was deleted, and the N-terminal presequence alone was not capable of transporting a fused passenger protein, Chinese hamster DHFR. YmL13 protein, on the other hand, was not transported without its N-terminal presequence, and its presequence was capable of transporting Chinese hamster DHFR into mitochondria. Thus, MRP7 appears to possess a transport signal in its mature part, while YmL13 possesses a signal only in its N-terminal presequence.