The amino-terminal half of pp59c-fyn contains sequences necessary for formation of a 75 kDa form and also repressive elements absent in pp60c-src.
Members of the src family of tyrosine kinases are composed of amino acid sequences which can be divided into three regions: the unique amino-terminal 80 residues; the next 180 residues of conserved but non-catalytic sequence; and the catalytic carboxy-terminal half of the molecule. To characterize the elements that regulate the catalytic and transforming activities of two members of this family, pp59c-fyn and pp60c-src, we generated six chimeric proteins by interchanging the three regions of the 531F mutant of pp59c-fyn and of the 527F mutant of pp60c-src. Our data indicate that substituting all or part of the amino-terminal 263 residues of pp59c-fyn for those of 527F inhibited the kinase and transforming activities of 527F. Conversely, substituting the amino-terminal half of pp60c-src for that of 531F resulted in an increase in the transforming potential of 531F. These results suggest that the amino-terminal half of pp59c-fyn contains elements which act to suppress the catalytic and transforming activities of the enzyme and that these suppressive elements are either absent or inactive in pp60c-src. These differences argue that the src family of tyrosine kinases are regulated differently in the cell. In vitro translation of some of the chimeras in rabbit reticulocyte lysates generated a 75 kDa protein in addition to the expected 59 kDa product. This 75 kDa species is analogous to the p75 protein previously detected in wild-type pp59c-fyn translation products. Interestingly, formation of p75 required the presence of DNA sequences encoding the unique amino-terminal residues of pp59c-fyn.
Espino
P C
PC
Laboratory of Cellular Regulation, Genzyme Corporation, Framingham, Massachusetts 01701.
Chou
W Y
WY
Smith
A E
AE
Cheng
S H
SH
D000818:Animals; D001483:Base Sequence; D002471:Cell Transformation, Neoplastic; D002645:Chickens; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D010449:Peptide Mapping; D011505:Protein-Tyrosine Kinases / Q000737:chemistry* / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000737:chemistry*; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000737:chemistry*; D011993:Recombinant Fusion Proteins; D013329:Structure-Activity Relationship
D009838:Oligodeoxyribonucleotides; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src)