Unusual Neutral Oligosaccharides in Mature Sindbis Virus Glycoproteins are Synthesized from Truncated Precursor Oligosaccharides in Chinese Hamster Ovary Cells

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Abstract
The presence of unusual small asparaginyl-oligosaccharides [(Man)3GlcNAc2-ASN] were demonstrated in the mature glycoproteins of Sindbis virus released from both wild-type and lectin-resistant Chinese hamster ovary cells, but the mechanism of synthesis of these structures was not determined. Gel filtration and endo-.beta.-N-acetylglucosaminidase analyses of pronase-digested glycopeptides from [3H]mannose-labeled Sindbis virus released at different times after infection of a phytohemagglutinin-resistant line of Chinese hamster ovary cells demonstrated that these small asparaginyl-oligosaccharides were present in similar relative amounts in virus released throughout the virus infection, rather than arising primarily at late times when cytopathic effects were maximal. Similar analyses of pulse-labeled, cell-associated viral glycopeptides suggested that these small oligosaccharides on mature virus glycoprotein resulted from the normal .alpha.1,2-mannosidase processing of truncated precursor oligosaccharides (containing 5 rather than 9 mannoses), rather than from aberrant processing or degradation of the full-size precursor oligosaccharides or normal intermediates.