Intracellular phosphorylation of the Sendai virus P protein.
Phosphorylation status of the Sendai virus P protein was examined during virus infection and compared with cell-free phosphorylation. P protein from Sendai virus-infected (VI) and P/C gene-transfected (PT) mammalian cells and from purified virions (PV) was phosphorylated at only serine residues. In contrast, cell-free phosphorylation of the P protein with virion-associated protein kinase (VAPK) occurred at both threonine and serine. Tryptic phosphopeptide maps of the P protein from VI, PT, and PV showed that the phosphorylation was primarily localized on one peptide (TP1), while VAPK phosphorylated the P protein on several peptides. There was no change in the steady-state phosphopeptide map of the P protein during virus replication, indicating that the TP1 is constitutively phosphorylated. Inhibition of cellular phosphatases (PP1 and PP2A) by okadaic acid (OA) in virus-infected cells caused a sixfold increase in the P protein phosphorylation, solely at serine residues. The phosphopeptide map of the OA-P protein revealed that phosphorylation occurred on several peptides, but the OA-P map was significantly different from the VAPK-P map. However, additional phosphorylation of the P protein did not block its association with nucleocapsids. These results suggest that the Sendai virus P protein is constitutively phosphorylated primarily at one locus but has the potential for phosphorylation at additional sites. Further, our results do not show any correlations between the intracellular and cell-free phosphorylation of the P protein and, therefore, question the validity of cell-free phosphorylations.
Byrappa
S
S
Department of Immunology/Microbiology, Rush Presbyterian St. Luke's Medical Center, Chicago, Illinois 60612, USA.
Hendricks
D D
DD
Pan
Y B
YB
Seyer
J M
JM
Gupta
K C
KC
D000818:Animals; D019556:COS Cells; D002474:Cell-Free System; D010750:Phosphoproteins / Q000502:physiology*; D010766:Phosphorylation; D029082:Sendai virus / Q000502:physiology*; D014764:Viral Proteins / Q000502:physiology*; D014779:Virus Replication
C055859:P protein, Sendai virus; D010750:Phosphoproteins; D014764:Viral Proteins