CTK - A PROTEIN-TYROSINE KINASE RELATED TO CSK THAT DEFINES AN ENZYMEFAMILY

We used the polymerase chain reaction with degenerate oligonucleotide primers to search for Csk-related kinases. A cDNA coding for a Csk-lik e protein-tyrosine kinase was cloned from mouse brain and was designat ed ctk, for csk-type protein-tyrosine kinase. The 1.9-kb ctk mRNA was found to be expressed predominantly in brain and capable of encoding a 52-kDa protein-tyrosine kinase. The amino acid sequence of Ctk was fo und to possess 53% identity with mouse Csk, shared all the predicted s tructural features of Csk, and was capable of phosphorylating the carb oxyl-terminal conserved tyrosine of Src family members. Our results th ereby indicate that ctk represents a gene that defines a family of str ucturally and functionally related Csk-like protein-tyrosine kinases.