PAS-related domain (PRD) repeats mediate phytochrome dimerization. 

The PRD domain targets the Pfr form of phyB to the nucleus, although it lacks a canonical nuclear localization signal (NLS).

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Treadmilling

Because the critical concentrations for the two ends are different, at steady state the free ATP–G-actin will be intermediate between Cc+ and Cc - , so the (+)end will grow and the (-)end will lose subunits.

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The two ends of microfilament polymerize at different rates:

fast-growing end - plus end

slow-growing end - minus end

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Critical concentration (Cc)

minimal concentration of monomers at which filaments form

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The rate of addition of monomers is given by

rate constant kon (M–1 sec–1 )

The rate of loss is given by koff (sec–1)

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