Rb1

What is the Rb1 gene?

Retinoblastoma 1, also known as Rb1, is a tumor suppressor gene found on the long q-arm of chromosome 13, shown in the image above under the yellow arrow. Rb1 codes for the tumor suppressor protein pRb, which regulates the cell cycle.

Throughout the cell cycle, pRb can assume three different states-- unphosphorylated, hypophosphorylated, and hyperphosphorylated. In the G1 phase, pRb is hypophosphorylated with minimal phosphate attachment. Upon reaching restriction (R) point, pRb becomes hyperphosphorylated with increasing numbers of phosphate attachment until the end of M phase. Finally, as the cell cycle exits M phase, pRb is completely "stripped" of its phosphate attachments and resumes the unphosphorylated state. .



Different phophorylation states of pRb affects its activity and interaction with other cellular protiens. Hypophosphorylation of pRb renders pRb active, allowing it to bind and inhibit transcription factors such as E2F1 while promoting the proliferation of proteins that repress transcription. Active pRb keeps cells in G1 phase and prevents cells from replicating their DNA. On the other hand, hyperphosphorylation of pRb renders it inactive, so that pRb is no longer able to inhibit transcription factors. Uninhibited transcription factors entail for DNA replication as cells are promoted to pass the R point, enter S phase, and divide by mitosis. .

Some images are modified from Weinberg, R. (2007) The Biology of Cancer. New York, NY: Garland Science Taylor & Francis Group.

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