Cell-associated episialin is a complex containing two proteins derived from a common precursor.
cDNA for the epithelial sialomucin episialin encodes a transmembrane molecule with a large extracellular domain, which mainly consists of repeats of 20 amino acids. Here we confirm the existence of a previously proposed proteolytic cleavage of episialin that occurs in the endoplasmic reticulum (Hilkens, J., and Buijs, F. (1988) J. Biol. Chem. 263, 4215-4222) and show that a similar cleavage takes place in in vitro translation systems. Using in vitro translation of truncated mRNAs, we map the cleavage site to a region located between 71 and 53 amino acids upstream of the transmembrane domain. Analysis of a mutant, in which this region has been deleted, indicates that the cleavage sites used in vitro and in vivo are identical or in close proximity. Both cleavage products remain associated although they are not linked through disulfide bonds. Therefore, the subunit derived from the N terminus, which represents the actual mucin-like domain, remains indirectly anchored to the cell membrane as a result of its interaction with the C-terminal subunit.
Ligtenberg
M J
MJ
Division of Tumor Biology, The Netherlands Cancer Institute (Antoni van Leeuwenhoekhuis), Amsterdam.
Kruijshaar
L
L
Buijs
F
F
van Meijer
M
M
Litvinov
S V
SV
Hilkens
J
J
D000595:Amino Acid Sequence; D000906:Antibodies; D000951:Antigens, Neoplasm / Q000235:genetics; D001483:Base Sequence; D001943:Breast Neoplasms; D002460:Cell Line; D002872:Chromosome Deletion; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005260:Female; D014644:Genetic Variation; D005944:Glucosamine / Q000378:metabolism; D006801:Humans; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D018396:Mucin-1; D009838:Oligodeoxyribonucleotides; D009842:Oligopeptides / Q000138:chemical synthesis / Q000276:immunology; D016133:Polymerase Chain Reaction; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics; D011863:Radioimmunoassay; D015183:Restriction Mapping
D000906:Antibodies; D000951:Antigens, Neoplasm; D046911:Macromolecular Substances; D008562:Membrane Glycoproteins; D018396:Mucin-1; D009838:Oligodeoxyribonucleotides; D009842:Oligopeptides; D012333:RNA, Messenger; D004247:DNA; D005944:Glucosamine