RB1 (RB)

RB1, the retinoblastoma gene, encodes RB, a transcriptional corepressor that restrains entry into the cell cycle by holding E2F transcription factors inactive until growth signals justify division.

Function

RB binds E2F at promoters of S-phase genes and recruits chromatin modifiers that keep those promoters silent. Cyclin D–CDK4/6 and cyclin E–CDK2 phosphorylate RB as the cell commits to division; phosphorylation releases E2F, and the S-phase program runs. p16 blocks the phosphorylation step, which makes the CDK4/6–RB–E2F axis the cell’s main gate between G1 and S. In quiescent and senescent cells RB stays hypophosphorylated and the gate stays shut.

In cancer

RB1 takes its name from retinoblastoma, the childhood