Proteolytic processing of the primary translation product of rat intestinal apolipoprotein A-IV mRNA. Comparison with preproapolipoprotein A-I processing.

Total cellular RNA, isolated from rat intestinal epithelium, was translated in a wheat germ cell-free system, and the primary translation product of apolipoprotein A-IV mRNA was purified by immunoprecipitation with monospecific antibody. NH2-terminal sequence analyses of mature rat plasma high density lipoprotein-associated A-IV and the cell-free product revealed that A-IV is initially synthesized with a 20-amino-acid NH2-terminal extension. Co-translational cleavage of the primary translation product indicated that the entire NH2-terminal extension behaved as a prepeptide. The prepeptides of intestinal apolipoproteins A-I and A-IV have 59% sequence homology. However, A-IV does not possess the unusual propeptide previously identified in intestinal A-I (Gordon, J. I., Smith, D. P. Andy, R., Alpers, D. H. Schonfeld, G., and Strauss, A. (1982) J. Biol. Chem. 257, 971-978). Therefore it appears that proteolytic processing of these two apolipoproteins differs significantly.