In vivo phosphorylation and membrane association of the fyn proto-oncogene product in IM-9 human lymphoblasts.
The protein product of the src-related proto-oncogene, fyn, was isolated from IM-9 cells with antibodies specific for the amino-terminal 22 residues of the fyn protein. Peptide mapping demonstrated that the fyn protein was distinct from the closely related c-src and c-fgr proteins. The fyn protein from IM-9 cells incorporated [3H]myristate in vivo and was found to be membrane associated. Phosphoamino acid analysis demonstrated that the fyn protein from IM-9 cells was phosphorylated in vivo predominantly on tyrosine and threonine with only a small amount of phosphoserine detected. the major chymotryptic phosphopeptide of the fyn protein was phosphorylated exclusively on tyrosine. This peptide was specifically precipitated by antibodies directed against a peptide modeled on the closely related carboxy termini of the c-src and fyn proteins. These results provide direct evidence for phosphorylation of tyrosine-531 in the carboxy-terminal chymotryptic peptide of the fyn protein. Phosphorylation of the corresponding site in the closely related c-src protein (tyrosine-527) represses src kinase activity and transforming ability. Loss of the phosphorylation site at tyrosine-531 may similarly contribute to the transforming abilities of carboxy-terminal deletion mutants of the fyn protein.
Department of Biochemistry, University of New Hampshire, Durham 03824.
D J
DJ
Peters
B R
BR
McGrew
D C
DC
Perron
L M
LM
Liptak
A P
AP
Laudano
D000911:Antibodies, Monoclonal; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism*; D010766:Phosphorylation; D011233:Precipitin Tests; D011487:Protein Conformation; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000378:metabolism*; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000032:analysis / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism
D000911:Antibodies, Monoclonal; C000715470:MAS1 protein, human; D008565:Membrane Proteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D013912:Threonine; D014443:Tyrosine; D051076:Proto-Oncogene Proteins c-fyn; D016392:Proto-Oncogene Proteins pp60(c-src)