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a chemical element, atomic number 37, atomic weight 85.47, symbol Rb. (See Appendix 6.)
rubidium 82 a radioactive isotope of rubidium having a half-life of 1.273 minutes and decaying by positron emission. It is used as a tracer in positron emission tomography.


Symbol for rubidium.


A gene on chromosome 13q14.2 that encodes a tumour suppressor protein which is a key regulator of entry into cell division, promoting G0-G1 transition following phosphorylation by CDK3/cyclin-C. RB1 represses transcription of E2F1 target genes. Underphosphorylated,
active forms of RB1 interact with E2F1 and repress its transcription activity, leading to cell cycle arrest. With calcium influx, RB1 is dephosphorylated by calcineurin, leading to release of the repressor complex.  

Molecular pathology
Defects in RB1 cause childhood retinoblastoma, some forms of osteogenic sarcoma and increased susceptibility to bladder cancer.