Evolution of intestinal apolipoprotein B mRNA editing. Chicken apolipoprotein B mRNA is not edited, but chicken enterocytes contain in vitro editing enhancement factor (s)

Teng, B.; Davidson, N.O.

Journal of Biological Chemistry 267(29): 21265-21272


ISSN/ISBN: 0021-9258
PMID: 1400437
Accession: 002103909

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Mammalian intestinal apolipoprotein B (apoB) messenger RNA (mRNA) undergoes post-transcriptional editing, changing codon 2153 from CAA in apoB100 mRNA to an in-frame translational stop codon (UAA) in apoB48 mRNA. By contrast, fowl intestinal apoB cDNA contains a CAA codon at the corresponding site, and apoB mRNA from fowl enterocytes, kidney, and liver is unedited. The cDNA sequence of fowl apoB spanning the edited base was divergent from mammalian apoB cDNA sequence, with 70% homology over the conserved 29-nucleotide sequence (6662-6690) flanking codon 2153. Efficient in vitro editing of both human and rat, but not fowl, synthetic apoB RNA was achieved using rat enterocyte S-100 extracts. By contrast, fowl enterocyte S-100 extracts failed to edit fowl, rat or human synthetic apoB RNA. Mixing experiments, however, revealed that fowl enterocyte S-100 extracts enhance the in vitro editing activity of rat, pig and human enterocyte S-100 extracts upon homologous RNAs. The editing enhancement activity of fowl enterocyte S-100 extracts is tissue-specific, heat-sensitive, substrate-saturable, and sensitive to proteinase K, but resistant to micrococcal nuclease. The activity was partially purified by Q-Sepharose chromatography, and had an av. molecular mass of 49 kDa when analysed by gel filtration chromatography.