Two phosphorylated proteins having molecular weights of 57kD and 72kD were detected from the slubilized membrane protein fraction of mating type a cells of Rhodosporidium toruloides which belongs to heterobasidiomycetous yeast. The phosphorylation of the protein was inhibited by a sexual pheromone, Rhodotorucine A (Rh. A), which is secreted from mating type a cells. On the other hand, counterpart mating type A cells and M-39 strain which is a styerile mutant derived from a cells, had also the same two phosphorylated proteins, However, the phosphorylation of the protein from A cells, and M-39 strain were not inhibited by the Rh. A. It suggests that inhibition of the phosphorylation reaction by the Rh. A in mating type a cells is a mating-type-specific reaction that relate to transduction mechanism of sexual pheromone signaling