Two proteins essential for apolipoprotein B mRNA editing are expressed from a single gene through alternative splicing.
Apolipoprotein B (apoB) mRNA editing involves site-specific deamination of cytidine to form uridine, resulting in the production of an in-frame stop codon. Protein translated from edited mRNA is associated with a reduced risk of atherosclerosis, and hence the protein factors that regulate hepatic apoB mRNA editing are of interest. A human protein essential for apoB mRNA editing and an eight-amino acid-longer variant of no known function have been recently cloned. We report that both proteins, henceforth referred to as ACF64 and ACF65, supported APOBEC-1 (the catalytic subunit of the editosome) equivalently in editing of apoB mRNA. They are encoded by a single 82-kb gene on chromosome 10. The transcripts are encoded by 15 exons that are expressed from a tissue-specific promoter minimally contained within the -0.33-kb DNA sequence. ACF64 and ACF65 mRNAs are expressed in both liver and intestinal cells in an approximate 1:4 ratio. Exon 11 is alternatively spliced to include or exclude 24 nucleotides of exon 12, thereby encoding ACF65 and ACF64, respectively. Recognition motifs for the serine/arginine-rich (SR) proteins SC35, SRp40, SRp55, and SF2/ASF involved in alternative RNA splicing were predicted in exon 12. Overexpression of these SR proteins in liver cells demonstrated that alternative splicing of a minigene-derived transcript to express ACF65 was enhanced 6-fold by SRp40. The data account for the expression of two editing factors and provide a possible explanation for their different levels of expression.
Dance
Geoffrey S C
GS
Departments of Biochemistry and Biophysics, University of Rochester, Rochester, NY 14642, USA.
Sowden
Mark P
MP
Cartegni
Luca
L
Cooper
Ellen
E
Krainer
Adrian R
AR
Smith
Harold C
HC
D000071479:APOBEC-1 Deaminase; D017398:Alternative Splicing; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D003564:Cytidine Deaminase / Q000235:genetics* / Q000502:physiology; D018076:DNA, Complementary; D005091:Exons; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics* / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics
D018076:DNA, Complementary; D020033:Protein Isoforms; D012333:RNA, Messenger; D000071479:APOBEC-1 Deaminase; C000605089:APOBEC1 protein, human; D003564:Cytidine Deaminase