Open reading frame III of Borna disease virus encodes a nonglycosylated matrix protein

The open reading frame III of Borna disease virus (BDV) codes for a protein with a mass of 16 kDa, named p16 or BDV-M. p16 was described as an N-glyco sylated protein in several previous publications and therefore was termed g p18, although the amino acid sequence of p16 does not contain any regular c onsensus sequence for N glycosylation. We examined glycosylation of p16 and studied its membrane topology using antisera raised against peptides, whic h comprise the N and the C termini. Neither an N- nor a C-terminal peptide is cleaved from p16 during maturation. Neither deglycosylation of p16 by en doglycosidases nor binding of lectin to p16 was detectable. Introduction of typical N-glycosylation sites at the proposed sites of p16 failed in carbo hydrate attachment. Flotation experiments with membranes of BDV-infected ce lls on density gradients revealed that p16 is not an integral membrane prot ein, since it can be dissociated from membranes. Our experimental data stro ngly suggest that p16 is a typical nonglycosylated matrix protein associate d at the inner surface of the viral membrane, as is true for homologous pro teins of other members of the Mononegavirales order.