Biosynthesis of apolipoprotein C-III in rat liver and small intestinal mucosa.
We have examined the biosynthesis of rat apolipoprotein C-III in the small intestine and liver. The primary translation product of its mRNA was recovered from wheat germ and ascites cell-free systems. Comparison of its NH2-terminal sequence with the NH2 terminus of plasma high density lipoprotein-associated apolipoprotein C-III showed that apo-C-III was initially synthesized as a preprotein with a 20 amino acid long NH2-terminal extension: Met-X-X-X-Met-Leu-Leu-X-X-Ala-Leu-X-Ala-Leu-Leu-Ala-X-Ala-X-Ala. Co-translational cleavage of the cell-free translation product by signal peptidase generated a polypeptide with the same NH2 terminus as the mature protein (X-Glu-X-Glu-Gly-Ser-Leu-Leu-Leu-Gly-Ser-Met). Therefore, this apolipoprotein does not undergo post-translational proteolytic processing like two other high density lipoprotein-affiliated proteins, proapo-A-I and proapo-A-II. The mRNA encoding apolipoprotein C-III comprises 0.4% of the translatable RNA species in adult rat liver and 0.14% of the translatable RNA species in small intestinal epithelium. Acute fat feeding with a triglyceride meal resulted in a 2-fold increase in intestinal preapo-C-III mRNA accumulation but no change in the levels of preproapo-A-I mRNA. Thus, the acute response of the apo-A-I and C-III genes to triacylglycerol absorption differs.
D000595:Amino Acid Sequence; D000818:Animals; D053305:Apolipoprotein C-III; D001053:Apolipoproteins / Q000235:genetics* / Q000302:isolation & purification; D001056:Apolipoproteins C; D007413:Intestinal Mucosa / Q000378:metabolism; D007421:Intestine, Small / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008970:Molecular Weight; D010944:Plants / Q000378:metabolism; D014176:Protein Biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D014908:Triticum / Q000378:metabolism
D053305:Apolipoprotein C-III; D001053:Apolipoproteins; D001056:Apolipoproteins C