Identification and characterization of c-raf phosphoproteins in transformed murine cells.
Protein products of the c-raf gene were detected and characterized in two transformed murine cells lines by immunoprecipitation analysis with raf-specific sera. Both proteins reacted with an antiserum directed to the carboxyl terminus of the c-raf coding region. The p48raf (Mr48,000) phosphoprotein was found in a cell line transformed by an LTR-activated c-raf gene (Mueller & Mueller, 1984). It was found to be phosphorylated on serine and threonine residues and became phosphorylated in immunoprecipitates when supplied with [gamma-32]ATP. In contrast, P74raf, which was detected into a spontaneously transformed 3T3 (R+/Cl 3) cell line and may represent the full-length gene product of c-raf, appeared to incorporate [32P]PO4 less efficiently in vivo and exhibited a barely detectable associated kinase activity in only half of the experiments. The p48raf is a transforming protein which, like P75gag-raf, lacks the amino-terminal region of the c-raf coding region. P74raf, which retains the amino-terminal region, differs from p48raf in its phosphorylation characteristics and may not be a transforming protein. These data are consistent with a model in which lack of amino-terminal sequences in the c-raf gene product p48raf may, in and of itself, suffice to make it a transforming protein.
Schultz
A M
AM
BRI-Basic Research Program, NCI-Frederick Cancer Research Facility, Maryland 21701.
Copeland
T
T
Oroszlan
S
S
Rapp
U R
UR
D000818:Animals; D002460:Cell Line; D002472:Cell Transformation, Viral; D007158:Immunologic Techniques; D051379:Mice; D008970:Molecular Weight; D010750:Phosphoproteins / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000378:metabolism*
D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D011494:Protein Kinases