The retinoblastoma susceptibility gene product undergoes cell cycle-dependent dephosphorylation and binding to and release from SV40 large T.
Synchronized monkey cells pulse-labeled with [35S]-methionine and chased for various lengths of time were extracted, and immunoprecipitations were performed using monoclonal antibodies directed against the retinoblastoma protein (RB) and SV40 T antigen (T). By following a discrete population of these two proteins through the cell cycle, the following information was obtained. RB, which is wholly unphosphorylated in G1, became phosphorylated at the beginning of S and remained phosphorylated through S and G2. RB was, then, completely dephosphorylated between the end of G2 and the beginning of G1. Second, while all of the detectable unphosphorylated RB can be found complexed with T, these complexes present during G1 dissociated in S and reformed again in M or early G1. Finally, T molecules appeared to oligomerize prior to binding RB. Thus, complex formation between T and RB may be regulated in part by the cell cycle-dependent phosphorylation and dephosphorylation of RB and by the quaternary structure of T.
Ludlow
J W
JW
Dana-Farber Cancer Institute, Boston, Massachusetts 02115.
Shon
J
J
Pipas
J M
JM
Livingston
D M
DM
DeCaprio
J A
JA
D000818:Animals; D000911:Antibodies, Monoclonal; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics*; D002453:Cell Cycle; D002460:Cell Line; D004261:DNA Replication; D004198:Disease Susceptibility; D005134:Eye Neoplasms / Q000235:genetics*; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D012175:Retinoblastoma / Q000235:genetics*; D016160:Retinoblastoma Protein; D013539:Simian virus 40 / Q000235:genetics / Q000276:immunology; D014162:Transfection
D000911:Antibodies, Monoclonal; D000952:Antigens, Polyomavirus Transforming; D009687:Nuclear Proteins; D010750:Phosphoproteins; D016160:Retinoblastoma Protein