APOBEC
[image:Apobec.J.Steinfeld.D.png|300px|thumb|upright|Example of a member of the APOBEC family, APOBEC-2. A cytidine deaminase from Homo sapiens.]
APOBEC is a family of evolutionarily conserved cytidine deaminases.
Function
A mechanism of generating protein diversity is mRNA editing. The APOBEC family of proteins perform mRNA modifications by deaminating cytidine bases to uracil. The N-terminal domain of APOBEC-like proteins is the catalytic domain, while the C-terminal domain is a pseudocatalytic domain. More specifically, the catalytic domain is a zinc dependent cytidine deaminase domain and is essential for cytidine deamination. The positively charged zinc ion in the catalytic domain attracts to the partial-negative charge of RNA.In the case of APOBEC-1, the mRNA transcript of intestinal apolipoprotein B is altered. RNA editing by APOBEC-1 requires homodimerization and this complex interacts with RNA-binding proteins to form the editosome. The resulting structure interacts with the codon CAA at codon 2153 and deaminates it into UAA, producing a stop codon that results in mRNA that is translated into the intestinal apoB-48 isoform. For other APOBEC-modified transcripts such as in the site-specific deamination of a CGA to a UGA stop codon in neurofibromatosis type 1 mRNA, the resulting proteins are predicted to be truncated as well, although these transcripts are possibly degraded.
C-to-U modifications do not always result in the truncation of proteins. For example, in humans/mammals they help protect from viral infections. APOBEC family proteins are widely expressed in cells of the human innate immune system.