The nucleosome has an approximate twofold axis of symmetry, called the dyad axis.

TLS Online TPP Program

#Id: 1365

#Unit 4. Cell Communication and Cell Signaling

JAK kinases phosphorylate several tyrosine residues on the cytosolic domain of the cytokine receptor.

TLS Online TPP Program

#Id: 1366

#Unit 4. Cell Communication and Cell Signaling

Phosphotyrosines function as docking sites for STAT proteins.

TLS Online TPP Program

#Id: 1367

#Unit 4. Cell Communication and Cell Signaling

All STAT proteins contain: 

An N-terminal DNA-binding domain

An SH2 domain

TLS Online TPP Program

#Id: 1368

#Unit 4. Cell Communication and Cell Signaling

In both RTKs and cytokine receptors, short amino acid sequences containing a phosphotyrosine residue are bound by signal-transducing proteins with conserved SH2 domains.

TLS Online TPP Program

#Id: 1369

#Unit 4. Cell Communication and Cell Signaling

The SH2 domain binds strongly to a critical four-residue core sequence containing peptide:  Phosphotyrosine–glutamic acid–glutamic acid–isoleucine

TLS Online TPP Program

#Id: 1370

#Unit 4. Cell Communication and Cell Signaling

Binding resembles the insertion of a two-pronged “plug”—the phosphotyrosine and isoleucine side chains of the peptide—into a two-pronged “socket” in the SH2 domain.