Molecular and genetic evidence for a virus-encoded glycosyltransferase involved in protein glycosylation.
The major capsid protein, Vp54, of chlorella virus PBCV-1 is a glycoprotein that contains either one glycan of approximately 30 sugar residues or two similar glycans of approximately 15 residues. Previous analysis of PBCV-1 antigenic mutants that contained altered Vp54 glycans led to the conclusion that unlike other glycoprotein-containing viruses, most, if not all, of the enzymes involved in the synthesis of the Vp54 glycan are probably encoded by PBCV-1 (I.-N. Wang et al., 1993, Proc. Natl. Acad. Sci. USA 90, 3840-3844). In this report we used molecular and genetic approaches to begin to identify these virus genes. Comparing the deduced amino acid sequences of the putative 375 PBCV-1 protein-encoding genes to databases identified seven potential glycosyltransferases. One gene, designated a64r, encodes a 638-amino-acid protein that has four motifs conserved in "Fringe type" glycosyltransferases. Analysis of 13 PBCV-1 antigenic mutants revealed mutations in a64r that correlated with a specific antigenic variation. Dual-infection experiments with different antigenic mutants indicated that viruses that contained wild-type a64r could complement and recombine with viruses that contained mutant a64r to form wild-type virus. Therefore, we conclude that a64r encodes a glycosyltransferase involved in synthesizing the Vp54 glycan. This is the first report of a virus-encoded glycosyltransferase involved in protein glycosylation.
Graves
M V
MV
Department of Plant Pathology, University of Nebraska, Lincoln, Nebraska, 68583-0722, USA.
Bernadt
C T
CT
Cerny
R
R
Van Etten
J L
JL
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004279:DNA, Viral; D015870:Gene Expression; D006031:Glycosylation; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010247:Paramecium / Q000821:virology; D017862:Phycodnaviridae / Q000201:enzymology* / Q000235:genetics; D011134:Polysaccharides / Q000737:chemistry; D011995:Recombination, Genetic; D014764:Viral Proteins
D004279:DNA, Viral; D011134:Polysaccharides; D014764:Viral Proteins; D016695:Glycosyltransferases; C432103:A64R protein, Paramecium bursaria Chlorella virus 1