APO B48 & APO B100 is synthesized from the same rnRNA; the difference between them is due to:
C i.e. Deamination of cytidine to uridine IRef: Vasudevan - Least post translational modification occurs in prokaryotic mRNA, which is generally identical to its primary transcript. Post translational modification of t-RNA includes removal of introns from anticodon loop, trimming of 5' & 3' ends, methylation / reduction / deamination / alkylation / rearranging glycolsidic bond to produced modified bases like methylated bases, dihydrouracil (D) & pseudo uracil (W) bases in nucleus, whereas cleavage and attachment of CCA tailing occur in cytoplasmQ. - In RNA, gene during processing undergoes nucleoside modifications, nucleoside cleavage and terminal addition but not chemical hydrolysisQ. - Post translational modification of mRNA involves 5' capping , 3' polyadenylation (addition of poly 'A' tail at 3' end), splicing (removal of non coding intervening or intron sequences and ligation / joining of coding exons) by Sn RNA/ Sn RNPs / Snurps or self splicing d/t ribozyme activity of self splicing introns with formation of lariat intermediates, RNA editing and secondary methylationQ. Apo B-48 and Apo B-100 are synthesized from same Apo B gene and same ApoB- m-RNA. Apo B 100 is a 100 kDa protein synthesized in liver by full length translation of corresponding mRNA of Apo B gene. Apo - B-100 forms pa of LDL, IDL and VLDL. Apo B-48 is a 48 KDa protein (48% shoer form of Apo B-100) synthesized in intestine by paial translation of same mRNA of Apo B gene. Apo B 48 forms pa of chylomicron & chylomicron remnant. This difference between the sizes of Apo B100 and Apo B48 occurs because post transcriptional processing (editing) of Apo B mRNA , deaminates the cytidine (C) to uracil (U) in intestine at 2153 position. After cyti dine deamination the CAA codon (which codes glutamine in liver) becomes UAA (nonsense or stop codon) in intestine. This results in shoer apo B-48 protein being made in intestine (and incorporated into chylomicron) than is made in the liver full length Apo B-100, incorporated in to VLDL.
RNA splicing
Allelic exclusion
Deamination of cytidine to uridine
Upstream repression