The shorter form, apo b48, arises by posttranscriptional rna editing whereby cytidine deamination produces a uaa termination codon. Full text get a printable copy pdf file of the complete article 1. A novel form of rna editing generates two forms of apolipoprotein b apob mrna by converting c at nucleotide 6666 to u. Apolipoprotein b rna editing enzymedeficient mice are viable.
While all the functional roles of apob within the ldl and all larger particles remain somewhat unclear, it is the primary organizing protein. Third, apo b48 could be produced by proteolytic cleavage of apo b100. Pdf apobec1 and apolipoprotein b mrna editing wenhsiung. Apob mrna editing is developmentally regulated in human fetal small intestine, producing parallel changes in the syn. Apolipoprotein apo b circulates in two distinct forms, apob100 and apob48. Gifforda, sooyon rheea, nicolas erikssonb, tommy f. This generates a stop translation codon and defines the carboxyl terminus of apolipoprotein b48. Apolipoprotein apo b mrna editing consists of a c u conversion of the first base of the codon caa encoding glutamine 2153 in apob mrna to uaa, a stop.
The catalytic subunit of the editing enzyme, apobec1, is an rnabinding cytidine deaminase that requires auxiliary factors for the editing of apob mrna. Pdf apolipoprotein apo b mrna undergoes a novel tissuespecific editing reaction, which replaces a genomically templated cytidine with uridine. Characterization of the apolipoprotein b mrna editing. The ctou editing of apolipoprotein b apo b mrna is catalyzed by a multiprotein complex that recognizes an 11nucleotide mooring sequence downstream of the editing site. Apobec1 expression varies throughout development, and apo b editing levels vary correspondingly. The subcellular compartment in which apolipoprotein apo b mrna is edited is unknown. Apolipoprotein b mrna editing is an intranuclear event.
Apolipoprotein apo b48 is produced in the mammalian intestine by a tissuespecific rna editing mechanism, which mediates a c to u conversion at position 6666 in apob mrna. Nov 25, 1992 in vitro apolipoprotein b mrna editing. A cdna encoding the hamster apob mrna editing enzyme was obtained by reverse transcriptasepolymerase chain reaction rtpcr and. Pdf sequence requirements for apolipoprotein b rna editing. Editing in vitro of apo b rna previously we have established a sensitive primer extension assay for the editing of apo b rna and have developed a system in vitro for rna editing. Jul 11, 1991 the editing of apo b mrna has little similarity to complex mrna processing events such as splicing and unlike editing in kinetoplastid protozoa does not utilise guide rnas. Host cellular factor apolipoprotein b messenger rna mrna editing enzyme catalytic polypeptidelike 3g ha3g is a cytidine deaminase that inhibits a group of viruses including human immunode. Chang a, makoto nakamuta a, wenhsiung li b, louis c.
An additional editing site is present in apolipoprotein b mrna. Characterization of apolipoprotein b mrna editing from. Apolipoprotein b48 an overview sciencedirect topics. Sequence editing by apolipoprotein b rnaediting catalytic.
Apr 30, 2012 apolipoprotein b apo b messenger rna mrna. Cytidine to uridine editing of apolipoprotein b apob mrna requires the cytidine deaminase apobec1 as well as a tripartite sequence motif flanking a target cytidine in apob mrna and an undefined number of auxiliary proteins that mediate rna recognition and determine sitespecific editing. Developmental regulation of apolipoprotein b mrna editing is. Apolipoprotein b is the main protein component of ldl cholesterol, comprising 95 per cent of its total protein content. Host apolipoprotein b messenger rnaediting enzyme catalytic. Apob rna editing is eliminated following targeting of apobec1, establishing that. Molecular cloning of apobec1 complementation factor, a. Second, a primary rnatranscript derived from the apo bgenecouldbedifferentially spliced to produce either apo b100 or apo b48 mrnas. Mouse apolipoprotein b editing complex 3 apobec3 is expressed in germ cells and interacts with deadend dnd1 chitralekha bhattacharya, sita aggarwal, madhu kumar, amatul ali, angabin matin department of cancer genetics, university of texas, md anderson cancer center, houston, texas, united states of america abstract background. Apolipoprotein apob circulates in two distinct forms, apob100 and apob48. The c to u editing of apolipoprotein b apob mrna converts a glutamine codon in apob100 mrna into a stop translation codon thereby generating apob48. Pdf molecular cloning of an apolipoprotein b messenger rna. Developmental and agerelated changes in apolipoprotein b mrna.
Computer modeling and ribonuclease probing of the wildtype and mutant apob rna. A solution of rabbitderived anti apo b antibody is incubated with the specimen. Apob mrna editing is mediated by a coordinated modulation of. Apolipoprotein b messenger rna editing is developmentally. Characterization of the apolipoprotein b mrna editing enzyme. A 40 kilodalton rat liver nuclear protein binds specifically to apolipoprotein b mrna around the rna editing site. A 27kda rat intestinal protein that does not itself edit apolipoprotein b mrna, but confers editing activity on chick intestinal extracts that do not have intrinsic editing activity, has. Apolipoprotein a1 apoa1 is the primary protein component of highdensity lipoprotein hdl. Sequence editing by apolipoprotein b rna editing catalytic component b and epidemiological surveillance of transmitted hiv1 drug resistance robert j. Recently, we have proposed the mooring sequence model, in which editing complexes editosomes assemble on specific apob mrna flanking sequences to direct this sitespecific editing event. The shorter form, apo b48, arises by posttranscriptional rna editing whereby cytidine deamination. Molecular cloning of apobec1 complementation factor, a novel. Apolipoprotein b apob mrna is edited in rat liver and intestine through the direct conversion of cytidine to uridlne at nucleotide 6666. The evolution of apolipoprotein b and its mrna editing.
These proteins can redistribute to other lipoprotein classes within serum as. Apo b is necessary for the reaction with ldl receptors in the liver and on cell walls, so it is involved in transporting cholesterol from the liver to the. B 100 and apo b 48 are encoded by the same apo b gene, with apo b 48 representing the aminoterminal 48% of apo b 100. The main catalytic peptide is apo b rna editing cytidine deaminase subunit 1 apobec1. Apolipoprotein b apob is the main structural and receptorbinding component of atherogenic lipoproteins in the very lowdensity lipoprotein vldl pathway, including ldlc. The catalytic subunit of the editing enzyme, apobec1, has cytidine deaminase activity but requires additional unidenti. Aug 30, 2019 validation of a sensitive assay and developmental biology of rna editing in the rat.
Apobec3 genes belong to a family of genes that encode dna and rna editing enzymes 16. Rna editing activity was demonstrated in both nuclear and cytoplasmic extracts. Apolipoprotein b mrnaediting protein induces hepatocellular. The intensity of the scattered light is directly proportional to the concentration of apo b in the specimen. We studied the site of endogenous apob mrna editing and correlated the extent of editing with mrna maturation in the rat liver. The evolution of apolipoprotein b apob has been intensely researched due to its importance during lipid transport. Apolipoprotein apo b mrna editing is the deamination of cytidine that. Apolipoprotein b is the primary apolipoprotein of chylomicrons, vldl, lpa, idl, and ldl particles ldl known commonly by the misnomer bad cholesterol when in reference to both heart disease and vascular disease in general, which is responsible for carrying fat molecules, including cholesterol, around the body to all cells within all tissues. Pdf mouse apolipoprotein b editing complex 3 apobec3 is. Apolipoprotein apo b48 is synthesized by mammalian small intestine as a result of posttranscriptional rna editing. Commitment of apolipoprotein b rna to the splicing pathway. Promiscuous guanine g to adenine a substitutions catalysed by apolipo.
The p27 catalytic subunit of the apolipoprotein b mrna. Get a printable copy pdf file of the complete article 1. These proteins can redistribute to other lipoprotein classes within serum as chylomicrons transfer their lipid content to cells and interacting lipoproteins. Pdf sequence requirements for the editing of apolipoprotein. The putative new editing site at position 6802 was examined for editing in vitro on a 482nucleotide rna representing an rsa i restriction fragment spanning. Davidson, in physiology of the gastrointestinal tract fourth edition, 2006. Dna sequence analysis of the gene that mediates this sitespecific cytidine deamination suggests that apo b mrna editing is an evolutionary adaptation to limit. Plasma apolipoprotein b48, hepatic apolipoprotein b mrna. Sequence requirements for the editing of apolipoprotein b mrna. Characterization of apolipoprotein b mrna editing from rabbit. In addition, we find that human apo b synthesis is also under developmental control. A fulllength complementary dna clone encoding an apo b messenger rna editing protein repr was isolated from rat small intestine. Developmental regulation of apolipoprotein b mrna editing. Specificity of the cytidine deamination is determined by the primary sequence of the apo b rna transcript, particularly an 11base mooring sequence, located just four nucleotides downstream of the edited site.
Nov 01, 2001 a tripartite motif located in the centre of the 7. Other cisacting elements include a 5 nucleotide spacer. Pdf sequence editing by apolipoprotein b rnaediting. In addition, hepatic apob mrna abundance as well as editing in the liver and intestine. An immune complex forms between the antibody and the apo b in the specimen, resulting in an increase in light scatter. Pdf an additional editing site is present in apolipoprotein. The c to u editing of apolipoprotein b apob mrna is mediated by a minimal complex composed of an. Several groups have reported northern blots showing two apo b mrnas in the small intestine, an.
Secondary structure for the apolipoprotein b mrna editing. This modification is most likely catalyzed by a nucleotide sequencespecific cytidine deaminase. Apolipoprotein b mrna editing catalytic polypeptide. Mammalian apolipoprotein b apo b exists in two forms, each the product of a single gene. Sequence editing by apolipoprotein b rna editing catalytic component b and epidemiological surveillance of transmitted hiv1 drug resistance robert shafer introductionsince 1991, it has been observed that hiv1 sequences occasionally contain an excess of guanine g to adenine a substitutions 1234. This test measures the amount of apo b in the blood. Apolipoproteins combine with lipids to transport them throughout the.
A novel mechanism involving editing of the apob mrna causes the formation. Apolipoprotein b mrna editing is an intranuclear event that occurs. Aid has the highest sequence homology with the apolipoprotein b apob mrna editing catalytic polypeptide 1 apobec1, which edits a specific cytidine on. Apolipoprotein b mrna editing is developmentally regulated in the human and rodent small intestine, changing from apolipoprotein b 100 also called apolipoprotein b or apo b is a protein that is involved in the metabolism of lipids and is the main protein constituent of lipoproteins such as very lowdensity lipoprotein vldl and lowdensity lipoprotein ldl, the bad cholesterol. Apolipoprotein b mrna editing enzyme catalytic polypeptide. Activationinduced cytidine deaminase shuttles between. Murine leukemia virus glycosylated gag blocks apolipoprotein. Pdf sequence requirements for apolipoprotein b rna. Three distinct rna sequence elements are required for. The messenger rna for apolipoprotein b undergoes a discrete and specific c to u editing of nucleotide 6666. Elevated apob and decreased apoa1 are associated with increased risk of cardiovascular disease. Molecular cloning of an apolipoprotein b messenger rna. Apolipoprotein b 100 also called apolipoprotein b or apo b is a protein that is involved in the metabolism of lipids and is the main protein constituent of lipoproteins such as very lowdensity lipoprotein vldl and lowdensity lipoprotein ldl, the bad cholesterol.
The editing of apo b rna is mediated by a novel cytidine deaminase. Although aid is required for dna cleavage 11, the detailed mechanism by which aid induces these genetic events is still under extensive debate. Apolipoprotein b mrna editing is an intranuclear event that. An in vitro system for the editing of apolipoprotein b mrna. Apobec1 is the first member of apobec to be identified and characterized as the apolipoprotein b editing complex 1, a protein that is involved in editing c to u of the apolipoprotein b pre. Mammalian fulllength apob100 can be posttranscriptionally edited by the enzyme apolipoprotein b mrna editing enzyme, catalytic polypeptidelike complexone apobec1 resulting in a truncated apob, known as apob48. Apob mrna editing is developmentally regulated in human fetal. The deadend dnd1 gene is essential for maintaining the. The small intestine of all mammals secretes apob48, which arises following ctou deamination of a single cytidine base in the nuclear apob transcript, introducing a translational stop codon. Aug 01, 2001 the editing of apolipoprotein b apob mrna is under tissuespecific, developmental and metabolic regulation.
Phosphorylation is a regulatory mechanism in apolipoprotein b. Regulation of intestinal apolipoprotein b mrna editing levels by a. While all the functional roles of apob within the ldl and. The human protein contains 236 amino acid residues and exists as a homodimer. Human liver secretes apob100, the product of a large mrna encoding 4536 residues. Apolipoprotein b mrna editing is developmentally regulated in the human and rodent small intestine, changing from apolipoprotein apo b48 is synthesized by mammalian small intestine as a result of posttranscriptional rna editing.
Apob mrna editing is a recent evolutionary development, roughly coinciding with the appearance of a lymphatic vasculature after the divergence of birds and reptiles, phyla that express exclusively unedited apob in the. Apolipoprotein b rna editing enzymedeficient mice are. Apolipoprotein b apob is the primary protein component of lowdensity lipoprotein ldl. We found that multiple protein kinase inhibitors or activators increased apob mrna editing up to 2. Mouse apolipoprotein b editing complex 3 apobec3 is expressed in germ cells and interacts with deadend dnd1. Apolipoprotein b rna editing enzymedeficient mice are viable despite alterations in lipoprotein metabolism. Smith a a departments of cell biology and medicine, baylor college of medicine, one baylor plaza, houston, tx 77030, usa b human genetics center, sph, unioersity of texas health science center at houston.
Editing is a site specific deamination event catalyzed by apob mrna editing catalytic subunit 1 apobec1 teng et al. Full text get a printable copy pdf file of the complete article 911k, or click on a page image below to browse page by page. Functional importance of intestinal apolipoprotein b messenger rna editing. This process is mediated by an enzyme complex containing a catalytic subunit, apobec1, which is homologous to other cytidine deaminases, particularly in a domain hcavex2430pcx2c which coordinates zinc. Pdf molecular cloning of an apolipoprotein b messenger. Develop mental and agerelated changes in apob mrna editing were studied using two mouse strains with. Human apolipoprotein apo b mrna undergoes a novel tissue specific editing reaction which replaces a genomically templated cytidine with uridine.
Ontogenetic regulation of apolipoprotein b mrna editing. Apr 25, 1991 apo b rna editing extracts from intestine did not edit maize cytochrome oxidase ii mrna. Mipomersen is an antisense oligonucleotide aso inhibitor of apob that inhibits the protein translation at the mrna level, thereby ultimately reducing ldlc levels. Host apolipoprotein b messenger rna editing enzyme catalytic polypeptidelike 3g is an innate defensive factor and drug target against hepatitis c virus zonggen peng, zhiyun zhao, yanping li, yuping wang, lanhu hao, bo fan, yuhuan li, yueming wang, yongqiang shan, yanxing han, yanping zhu, jianrui li, xuefu you, zhuorong li. Apolipoprotein b plasma levels, hepatic synthesis and secretion, and mrna abundance and editing in copperdeficient rats by scott kenneth reaves a dissertation submitted to the faculty of the commfitee on nutritional sciences in partial fulfillment of the requirements. Fasting is unnecessary both because of the relatively small contribution of apo b 48 containing lipoproteins to serum apo b and because epitopes for antibodies used in immunoassays that have been raised against apo b may be missing from apo b rupture of an atherosclerotic plaque may lead to thrombosis. Aid, like apobec1, conserves the catalytic motif of cytosine deaminase and has cytidine. Apolipoprotein b plasma levels, hepatic synthesis and. Apolipoprotein apo b occurs in two forms, apob100 512 kda and apob48 240 kda. An additional editing site is present in apolipoprotein b.
Jan 01, 1995 apolipoprotein apo b mrna editing consists of a c u conversion of the first base of the codon caa encoding glutamine 2153 in apob mrna to uaa, a stop codon. Multiple studies have reported that apob and apoa1 are more strongly associated with cardiovascular disease. Apolipoprotein b mrna editing and the reduction in synthesis and. Pdf mouse apolipoprotein b editing complex 3 apobec3.
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