B cells migrate to the lymphoid follicles. They are directed there by chemokine interactions between CXCL13, which is secreted by follicular dendritic cells (FDCs).

TLS Online TPP Program

#Id: 8620

#XL - R Botany

A second class of CKIs found in metazoan cells is the Cip/Kip family of CKIs, consists of three proteins—p21CIP, p27KIP1, and p57KIP2. 

TLS Online TPP Program

#Id: 8621

#XL - R Botany

The Cip/Kip family members bind to cyclin-bound CDKs and block the activity of cyclin D-, E-, A-, and B-containing complexes.

TLS Online TPP Program

#Id: 8622

#XL - R Botany

Cyclins are degraded through the action of two different E3-ligases:

1. SCF (Skp1, Cullin, and F-box proteins) 

2. APC/C or cyclosome

TLS Online TPP Program

#Id: 8623

#XL - R Botany

SCF and APC/C are multisubunit ubiquitin-protein ligases that belong to the RING finger family of ubiquitin-protein ligases.

TLS Online TPP Program

#Id: 8625

#XL - R Botany

Human SCF complexes contain: 

Three core components - Cul1 subunit, RBX1, Skp1 

and a substrate-targeting F-box protein

TLS Online TPP Program

#Id: 8626

#XL - R Botany

RBX1 is a RING finger–containing protein that binds the E2 ubiquitin-conjugating enzyme.