A class II gene is a type of

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

that codes for a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

. Class II genes are transcribed by

RNAP II RNA polymerase II (RNAP II and Pol II) is a multiprotein complex that transcribes DNA into precursors of messenger RNA (mRNA) and most small nuclear RNA (snRNA) and microRNA. It is one of the three RNAP enzymes found in the nucleus of eukaryo ...

. Class II genes have a promoter that may contain a

TATA box In molecular biology, the TATA box (also called the Goldberg–Hogness box) is a sequence of DNA found in the core promoter region of genes in archaea and eukaryotes. The bacterial homolog of the TATA box is called the Pribnow box which has ...

. Basal transcription of class II genes requires the formation of a preinitiation complex. They are transcribed by RNA polymerase II, include both intron and exon, and code for polypeptide. Major histocompatibility complex (MHC) class II genes are important in the immune response. Major histocompatibility complex (MHC) II is found on antigen-presenting cells (APCs) and functions to present exogenous proteins to CD4+ T cells. MHC II thus plays an important role in activating the immune system in response to extracellular pathogens via activation of CD4+ T cells. MHC class II molecules are differentially expressed across multiple cell-types. For example, MHC II molecules are constitutively expressed in thymic epithelial cells and antigen-presenting cells (APC's), whereas they undergo interferon-γ-mediated expression in other cell types. Central to the regulation of the complex gene-expression profile exhibited by MHC class II molecules is a single master regulatory factor known as the class II transactivator (CIITA). CIITA is a non-DNA-binding co-activator whose expression is tightly controlled by a regulatory region containing three independent promoters (pI, pIII and pIV).

References

Genes Molecular biology {{Gene-stub