Pause transfer: a topogenic sequence in apolipoprotein B mediates stopping and restarting of translocation.
Previously, we described the stepwise translocation of a large amino-terminal fragment of apolipoprotein B (apo B15) in which the nascent secretory chain translocates through a series of distinct, nonintegrated transmembrane intermediates with large domains exposed to the cytoplasm. Thus, apo B15 appears to stop and restart translocation at several points. We have identified a sequence of amino acids in apo B15 that confers this behavior on a heterologous chimeric protein. In addition, we dissect pausing into two distinct steps, stopping and restarting, thereby trapping otherwise transient intermediates. Finally, we demonstrate the function of a second "pause transfer" sequence over 200 amino acids downstream in apo B15 that restarts translocation posttranslationally, suggesting that multiple pause transfer sequences are involved in the biogenesis of apolipoprotein B.
Department of Microbiology and Immunology, University of California, San Francisco 94143-0444.
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D000595:Amino Acid Sequence; D000818:Animals; D001055:Apolipoproteins B / Q000235:genetics*; D001483:Base Sequence; D001798:Blood Proteins; D002417:Cattle; D015891:Cystatins / Q000235:genetics*; D005914:Globins / Q000235:genetics; D006023:Glycoproteins / Q000235:genetics*; D007425:Intracellular Membranes / Q000378:metabolism*; D008051:Lipid Bilayers; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D011388:Prolactin / Q000235:genetics; D014176:Protein Biosynthesis; D011487:Protein Conformation; D011499:Protein Processing, Post-Translational; D015183:Restriction Mapping; D014158:Transcription, Genetic; D060749:alpha-2-HS-Glycoprotein; D000509:alpha-Fetoproteins / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics
C071388:Ahsg protein, rat; D001055:Apolipoproteins B; D001798:Blood Proteins; D015891:Cystatins; D006023:Glycoproteins; D008051:Lipid Bilayers; D009838:Oligodeoxyribonucleotides; D060749:alpha-2-HS-Glycoprotein; D000509:alpha-Fetoproteins; D011388:Prolactin; D005914:Globins; D001618:beta-Lactamases