APOBEC1 complementation factor; APOBEC1-stimulating protein; apo B mRNA-targeting protein (ACF, ASP, A1CF)

Function

• component of the apolipoprotein B mRNA editing enzyme complex
• binds to APOB mRNA & is probably responsible for docking the catalytic subunit, APOBEC1
• interacts with KHSRP/KRSP, not required for APOBEC1 activity but may confer stability on the editing complex
• interacts with nuclear import protein TNPO2/TRN2 which may account for its transport into the nucleus

Structure

• contains 3 RRM domains (RNA recognition motif), necessary but not sufficient for binding to APOB mRNA additional residues in the pre-RRM & C-terminal regions are required for RNA-binding & for complementing APOBEC1 activity

Compartment

• nucleus, endoplasmic reticulum (ER), cytoplasm
• predominantly nuclear where it localizes to heterochromatin
• cytoplasmic, found at the outer surface of the ER
• shuttles between nucleus & cytoplasm
• may be transported into the nucleus by the nuclear import protein TNPO2/TRN2 or by APOBEC1

Alternative splicing

named isoforms=6

* isoforms 4 & 5 do not exhibit APOBEC1 complementation activity

Expression

• widely expressed
• highest levels in brain, liver, pancreas, colon, spleen
• mRNA-editing of apolipoprotein B allegedly occurs in small intestine

More general terms

• RNA-binding protein

Component of

• apolipoprotein B mRNA editing enzyme complex

Database

• UniProt: http://www.uniprot.org/uniprot/Q9NQ94.html