The nucleoprotein of marburg virus is target for multiple cellular kinases

The nucleoprotein (NP) of Marburg virus is phosphorylated at serine and thr eonine residues in a ratio of 85:15, regardless of whether the protein is i solated from virions or from eukaryotic expression systems. Phosphotyrosine is absent. Although many potential phosphorylation sites are located in th e N-terminal half of NP, this part of the protein is not phosphorylated. An alyses of phosphorylation state and phosphoamino acid content of truncated NPs expressed in Hela cells using the vaccinia virus T7 expression system l ed to the identification of seven phosphorylated regions (region I*, amino acids 404-432; II*, amino acids 446-472; III*, amino acids 484-511; IV*, am ino acids 534-543; V*, amino acid 549; VI*, amino acids 599-604; and VII*, amino acid 619) with a minimum of seven phosphorylated amino acid residues located in the C-terminal half of NP. All phosphothreonine residues and con sensus recognition sequences for protein kinase CKII are located in regions I*-V*. Regions VI* and VII* contain only phosphoserine with three of four serine residues in consensus recognition motifs for proline-directed protei n kinases. Mutagenesis of proline-adjacent serine residues to alanine or as partic acid did not influence the function of NP in a reconstituted transcr iption/replication system; thus it is concluded that serine phosphorylation in the most C-terminal part of NP is not a regulatory factor in viral RNA synthesis. (C) 1999 Academic Press.