Specification of the ectoderm is accomplished during gastrulation, by regulating the levels of BMP.

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#Unit 4. Cell Communication and Cell Signaling

GPK enzyme activity is increased either by phosphorylation of these two regulatory subunits by PKA or by Ca+2 binding to the calmodulin subunit; maximal activity requires both.

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#Unit 4. Cell Communication and Cell Signaling

Phosphorylation of PKA at threonine-197 leads to conformational change in the activation loop, that promotes binding of both ATP and its substrate proteins.

PKA can autophosphorylate itself on T197

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#Unit 4. Cell Communication and Cell Signaling

The activities of GPK and GP are inhibited by a phosphatase called phosphoprotein phosphatase.

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#Unit 4. Cell Communication and Cell Signaling

The promoter or enhancer segments of all genes regulated by PKA contain a cis-acting DNA sequence, the cAMP-response element (CRE), which

contains the highly conserved nucleotide sequence,

5'-TGACGTCA-3'.

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#Unit 4. Cell Communication and Cell Signaling

In nucleus PKA phosphorylate serine-133 on a transcription factor called CREbinding (CREB) protein

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#Unit 4. Cell Communication and Cell Signaling

Phosphorylated CREB binds to CRE-containing target genes and also binds to the co-activator termed CBP/P300, thereby stimulating gene transcription