RNA editing: a novel mechanism for regulating lipid transport from the intestine.
Human apolipoprotein (apo)-B mRNA undergoes a novel tissue specific editing reaction which replaces a genomically templated cytidine with uridine. This substitution converts codon 2153 from glutamine (CAA) in apo-B100 mRNA to a stop codon (UAA) in apo-B48 mRNA. This novel RNA editing process is responsible for the generation of hepatic apo-B100 and intestinal apo-B48. We have established the following concerning this process: (1) by transfection of a series of deletion mutants into the rat hepatoma cell line McArdle 7777, which makes both apo-B100 and apo-B48, we have defined a minimum sequence of 26 nucleotides that is required for apo-B mRNA editing. The sequence containing the modified nucleotide forms a 26 nucleotide highly conserved stem loop with the modified nucleotide occurring in an 8-base loop. (2) Conversion in vitro of apo-B mRNA has been established, using cell free S100 cytoplasmic extract and synthetic RNA templates. Activity was abolished by protease treatment. (3) Transgenic mice were created which expressed a human apo-B construct spanning the stop codon. Apo-B mRNA was found in all tissues examined and this was shown to undergo editing. (4) In the rat liver, which produces apo B-100 and apo-B48, modulation of the relative proportion of these proteins by thyroxine was demonstrated to be mediated at the level of the RNA editing mechanism. It is concluded that apo-B mRNA is edited by a generally expressed protein and editing is highly regulated.
Scott
J
J
Division of Molecular Medicine, MRC Clinical Research Centre, Harrow, Middx.
Wallis
S C
SC
Davies
M S
MS
Wynne
J K
JK
Powell
L M
LM
Driscoll
D M
DM
D000818:Animals; D001055:Apolipoproteins B / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D001692:Biological Transport; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D050356:Lipid Metabolism; D008099:Liver / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000378:metabolism*
D001055:Apolipoproteins B; D012333:RNA, Messenger