THE NOVEL ANTITUMOR NUCLEASE RC-PUP FROM RANA CATESBEIANA OOCYTES. Yen-Chywan Liaw^l, Faik N. Musayev^l, You-Di Liao², ¹Institute of Molecular Biology and ²Institute of Biomedical Science, Academia Sinica, Taipei, Taiwan, ROC

The crystal structure of RC-PUP, a pyrimidine-guanine sequence-specific ribonuclease which is isolated from Rana Catesbeiana (bullfrog) oocytes, has been determined. A number of anticancer proteins, which shown sequence highly homologous to RNase A, were recently found from frog eggs. These proteins are abundant in the frog oocytes and reveal cytotoxic ribonuclease activity, which they appear to bind to cells, enter the cytosol where they degrade the RNA and kill the target cells. It is very likely that exert this kind of cytotoxic ribonuclease as antiparasitic and anticancer agent in human.

The RC-PUP is crystallized in the space group P4₁, with cell dimensions a = 68.7 Å, b = 68.7 Å, and c = 52.3 Å and diffract up to 2.4 Å resolution. The structure was solved by molecular replacement method using P-30 protein (Onconase) as initial model. The overall folding is similar to other RNase. Three loop regions show different folding.

Many specific features of RC-PUP and this class of proteins are under investigation, such as, the protein cell binding and their cytotoxic mechanism. The detail refinement and comparism with other RNases is in progress.