CLONING AND CHARACTERIZATION OF CDNAS ENCODING A NOVEL NONRECEPTOR TYROSINE KINASE, BRK, EXPRESSED IN HUMAN BREAST-TUMORS

Using a polymerase chain reaction based differential screening approac h, we have isolated and characterised a cDNA from a human metastatic b reast tumour representing a novel protein tyrosine kinase (brk). Seque ncing of brk cDNAs isolated from T-47D and MCF-7 human breast tumour c ell lines indicate that they encode a protein with the features of a n ovel nonreceptor tyrosine kinase, including amino terminal SH3 and SH2 domains. When synthesised in recombinant baculovirus and bacterial ex pression systems, brk protein products are capable of autophosphorylat ion on tyrosine residues. Initial expression studies have detected low levels of brk transcripts in some human breast tumours and breast tum our cell lines, but not in normal breast tissue.