A RING FINGER MOTIF REGULATES TRANSFORMING ACTIVITY OF THE RFP RET FUSION GENE/

The rfp/ret transforming gene was generated by DNA rearrangement which occurred during transfection of NIH 3T3 cells. The amino-terminal hal f of Rfp with a RING finger motif was fused to the truncated Ret recep tor tyrosine kinase, leading to a transforming sequence, Rfp/Ret. In t he present study, to elucidate the importance of a RING finger motif f or its transforming activity, we mutated cysteine or histidine residue s present in the motif that are believed to be crucial for the tertiar y structure of the protein. Substitution of Cys-16, Cys-31, or His-33 markedly decreased the transforming activity of Rfp/Ret. These mutatio ns also resulted in a striking decrease of tyrosine phosphorylation of the mutant proteins in transfectants. In contrast, mutations of Cys-1 18 or His-124 in the second cysteine/histidine-rich motif (called B bo x) of Rfp/Ret did not affect its activity. These results thus indicate d that the RING finger structure is critical for the full transforming activity of Rfp/Ret. (C) 1996 Academic Press, Inc.