Small ncRNAs involved in RNA splicing in the spliceosome are trimethylated at terminal guanine. This structure is called a trimethylated cap. The enzymes for these additional methyl transfers are present in the cytoplasm.

TLS Online TPP Program

#Id: 1719

#Unit 4. Cell Communication and Cell Signaling

The other IgE receptor, designated FcεRII, or CD23, has a much lower affinity for IgE (Kd of 1 * 10 6 M -1 )

TLS Online TPP Program

#Id: 1720

#Unit 4. Cell Communication and Cell Signaling

Most cells express a tetrameric form of FcεRI, which includes an α and β chain and two identical disulfide-linked γ chains.

TLS Online TPP Program

#Id: 1721

#Unit 4. Cell Communication and Cell Signaling

Monocytes and platelets express an alternative form lacking the β chain.

TLS Online TPP Program

#Id: 1722

#Unit 4. Cell Communication and Cell Signaling

The α chains of the FcεRI, members of the immunoglobulin superfamily, directly bind the IgE heavy chains, whereas the β and γ chains are responsible for signal transduction.

TLS Online TPP Program

#Id: 1723

#Unit 4. Cell Communication and Cell Signaling

CD23a is found on activated B cells, whereas CD23b is induced on various cell types by the cytokine IL-4.

TLS Online TPP Program

#Id: 1724

#Unit 4. Cell Communication and Cell Signaling

CD23 binds not only to IgE, but also to the complement receptor CD21.