Co-translational processing and intracellular transport of rat salivary mucus glycoprotein.
A preparation of peptidyl-tRNA from intact microsomes of mucin-synthesizing polysomes of sublingual salivary gland cells contained fatty-acylated galactosamine-free and galactosamine-enriched peptidyl-tRNA fractions, whereas trypsin-chymotrypsin treated microsomes yielded predominantly the acylated galactosamine-enriched peptidyl-tRNA complexes. Radioscanning and chemical analyses revealed that palmitate was substituted on all nascent peptides, except those shorter than 20 amino-acid residues. In contrast, the [35S]-methionine label was detected only on galactosamine-free peptides containing up to 70 amino acids. On SDS-polyacrylamide gel, the peptides released from galactosamine-enriched tRNA complexes separated into a multitude of bands ranging in size from 6000 to 60,000 dalton, whereas the total preparation afforded peptides ranging from 2000 to 60,000 dalton. Pulse-chase experiments, using radiolabelled methionine, palmitic acid and N-acetylgalactosamine, combined with chemical characterization of the radiolabelled fatty acids and carbohydrates from purified peptidyl-tRNA, confirmed that the N-terminal fatty acylation and the initial O-glycosylation with N-acetylgalactosamine are the co-translational processes taking place as soon as peptide is sufficiently large to be acylated, trimmed, and translocated to the luminal site of endoplasmic membrane.
Slomiany
A
A
Dental Research Center, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark 07103.
Mizuta
K
K
Zalesna
G
G
Tsukada
H
H
Slomiany
B L
BL
D000215:Acylation; D000818:Animals; D006023:Glycoproteins / Q000378:metabolism*; D006031:Glycosylation; D008297:Male; D008715:Methionine / Q000378:metabolism; D010169:Palmitic Acids / Q000378:metabolism; D011132:Polyribosomes / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012470:Salivary Glands, Minor / Q000378:metabolism; D012471:Salivary Proteins and Peptides / Q000378:metabolism*
D006023:Glycoproteins; D010169:Palmitic Acids; D021382:Protein Sorting Signals; D012471:Salivary Proteins and Peptides; D012343:RNA, Transfer; D008715:Methionine