Functional expression of the yes proto-oncogene protein in Xenopus oocytes injected with chicken cerebellar mRNA.

Using monospecific antibodies raised against the amino terminal domain of viral-yes protein, we precipitated a 58 kD protein-tyrosine kinase from the brain of Xenopus laevis frog. By a number of criteria, including pattern of expression in various tissues and one-dimensional peptide mapping, we concluded that pp58 is very likely the authentic amphibian yes protein because it is more similar to the chicken yes protein than to any other known tyrosine kinases. The pp58c-yes is expressed in adult brain at elevated levels. In contrast, its level of expression in follicular and denuded oocytes is 30-50 times lower. Because of the low endogenous expression of the oocyte-associated yes kinase, we were able to transiently express and analyze pp62c-yes by injecting oocytes with 27S size fraction of poly(A)+ mRNA isolated from chicken cerebella. The pp62c-yes expressed in oocytes from the exogenous message comigrated on SDS polyacrylamide gel with pp62c-yes from cerebellum and was indistinguishable from it by one-dimensional peptide mapping. The pp62c-yes expressed in oocytes was enzymatically active. A number of phosphotyrosine-containing proteins were detected specifically in the c-yes mRNA-injected oocytes. The usefulness of the Xenopus oocyte expression system to study the functional aspects of c-yes protein and other tyrosine kinases was evaluated.