3 separate TGF-β receptor proteins participate in binding TGF-β and activating signaling:

RI, RII, and RIII

TLS Online TPP Program

#Id: 6380

#Unit 2. Cellular Organization

OC are constitutive because repressor protein is unable to bind; this allows RNA polymerase to have unrestrained access to the promoter.  The Oc mutations are cis-acting/cis dominant, because they affect only the contiguous set of structural genes.

TLS Online TPP Program

#Id: 6381

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6382

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6383

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 6384

#Unit 2. Cellular Organization

The DNA-binding domain occupies residues 1–59. It contains two a-helices separated by a turn. This is a common DNA-binding motif known as the HTH (helix-turn-helix); the two a-helices fit into the major groove of DNA

TLS Online TPP Program

#Id: 6385

#Unit 2. Cellular Organization

Promoter mutations are also cis-acting. If they prevent RNA polymerase from binding at P-lac, the structural genes are never transcribed.