lacZ encodes for b-galactosidase,a tetramer of 500 kD. The enzyme breaks lactose is cleaved into glucose and galactose.  This enzyme also produces an important byproduct, b-1,6-allolactase.

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#Unit 6. System Physiology – Plant

Pr chromophore undergoes a cis–trans isomerization between carbons 15 and 16 and rotation of the C14-C15 single bond on red light exposure.

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#Unit 6. System Physiology – Plant

Phytochromobilin is synthesized in plastids from chlorophyll biosynthetic pathway and transported into cytosol by a passive process.

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Phytochromobilin is exported from the plastid to the cytosol where it autocatalytically attaches to the PHY apoprotein through a thioether linkage to a cysteine residue.

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#Unit 6. System Physiology – Plant

hy1 and hy2 mutant are chromophore biosynthesis mutant: which fail to supress hypocotyl elongation

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#Unit 6. System Physiology – Plant

Pfr is the physiologically active forms of Phytochrome

Wild type: short hypocotyl by white light

hy mutant (phytochrome mutant): long hypocotyl by white light

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#Unit 6. System Physiology – Plant

A toggle model is for phytochrome interconversion

The structure of the b-hairpin region of Pr is changed to an a helix during the conversion of Pr to Pfr, which initiates other conformational changes in the protein.