In the dark, the maximum absorption of the FMN chromophore is around 450 nm. 

Blue light induces the formation of a covalent bond between FMN and a cysteine residue, shifting the absorption maximum to 390 nm via a LOV660 intermediate form. The reaction is reversible in darkness.

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#XL - R Botany

In vertebrates, Rb is the major guardian of the cell cycle, integrating information about DNA damage and cell growth

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Rb binds the activation domains of a E2F transcription factors, in the cytoplasm to prevent them from turning on the genes required for cell cycle progression.

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#XL - R Botany

TLS Online TPP Program

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When E2Fs are bound to Rb, not only are they transcriptionally inactive, but they also function to repress transcription by recruiting chromatin-modifying enzymes that promote deacetylation and methylation of specific histone lysines.

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Phosphorylation on multiple sites by G1 CDKs blocks Rb from associating with E2F and promotes its export out of the nucleus.

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Rb protein regulation by G1 CDKs in mammalian cells is analogous to Whi5 regulation by Cln3-CDK in yeast.