The SRP and the nascent polypeptide chain–ribosome complex bind to the SRP receptor in the ER membrane. This interaction is strengthened by the binding of GTP to both the SRP and its receptor.

TLS Online TPP Program

#Id: 8630

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 8631

#Unit 2. Cellular Organization

APC/C core is organized into three modules: 

1. a scaffold module 

2. a catalytic module

3. a substrate recognition module

TLS Online TPP Program

#Id: 8632

#Unit 2. Cellular Organization

Substrate-targeting subunits of the APC/C recognize specific sequence motifs on the proteins that the APC/C ubiquitinates. One motif, the destruction box or D-box, has the consensus sequence

RXXLX[D/E]ΦΦΦXN[N/S]

TLS Online TPP Program

#Id: 8633

#Unit 2. Cellular Organization

Mutating or deleting the destruction box in mitotic cyclins prevented their ubiquitination and blocked cells from exiting mitosis.

TLS Online TPP Program

#Id: 8634

#Unit 2. Cellular Organization

At the metaphase to anaphase transition, APC/C bound to Cdc20 targets cyclins A /B and securin for degradation.

TLS Online TPP Program

#Id: 8635

#Unit 2. Cellular Organization

During late anaphase, telophase and G1, APC/C bound to Cdh1 targets B type cyclins and geminin for degradation.