Western blot analysis of Rb-C Fusion Protein #6022 (amino acids 701-928 of Rb fused to MBP) before (-) and after (+) in vitro phosphorylation by cdc2/cyclin B Protein Kinase (New England Biolabs #P6020), using Phospho-Rb (Ser795) Antibody #9301 (left) or the control antibody (right).
Boil for 3 minutes prior to use. Load 10 μl (50 ng) of phosphorylated and nonphosphorylated Rb Control Proteins per lane.
Store at -20°C.
Nonphosphorylated Rb-C Fusion Protein (5 µg/ml): Rb-C is expressed as a recombinant fusion protein of Rb residues 701–928 and maltose binding protein serves as a negative control. Supplied in SDS Sample Buffer.
Phosphorylated Rb-C Fusion Protein (5 µg/ml): Rb-C is expressed as a recombinant fusion protein of Rb residues 701–928 and maltose binding protein prepared by in vitro kinase reaction with cdc2 serves as a positive control. Supplied in SDS Sample Buffer.
Note: This truncated Rb recombinant protein is not recognized by Phospho-Rb (Ser608) Antibody #2181 or Rb (D20) Rabbit mAb #9313.
Apparent Molecular Weight: Both the nonphosphorylated and phosphorylated forms of Rb-C migrate at an apparent molecular weight of 76 kDa by SDS-PAGE.
The retinoblastoma tumor suppressor protein Rb regulates cell proliferation by controlling progression through the restriction point within the G1-phase of the cell cycle (1). Rb has three functionally distinct binding domains and interacts with critical regulatory proteins including the E2F family of transcription factors, c-Abl tyrosine kinase, and proteins with a conserved LXCXE motif (2-4). Cell cycle-dependent phosphorylation by a CDK inhibits Rb target binding and allows cell cycle progression (5). Rb inactivation and subsequent cell cycle progression likely requires an initial phosphorylation by cyclin D-CDK4/6 followed by cyclin E-CDK2 phosphorylation (6). Specificity of different CDK/cyclin complexes has been observed in vitro (6-8) and cyclin D1 is required for Ser780 phosphorylation in vivo (9).
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