Measles virus gene expression in lytic and persistent infections of a human lymphoblastoid cell line

MOMP1 is a measles virus (MV) long-term steady-state persistently infected culture of the human T lymphoblastoid cell line MOLT4. The analysis of MV gene expression revealed that in MOMP1 cells, the major MV proteins, haemagglutinin (H), phosphoprotein (P), nucleoprotein, fusion (F) and matrix (M), are present and the fusion precursor (F0) is cleaved into F2 and F1 peptides. H and F2 proteins are glycosylated in both lytic and persistent MOLT4 infections. All major proteins are underexpressed in the persistently infected cultures in comparison to the lytically infected cells. However a relatively greater reduction was observed for H, M and P proteins. Pulse-chase labelling experiments indicated that this underexpression of H, M and P proteins was not due to selective degradation of these proteins in the persistent infection (p.i.). The relative amounts of the major monocistronic and dicistronic mRNAs for MV proteins, with the exception of P mRNA, was not altered in the p.i. with respect to lytically infected MOLT4 cells, suggesting that the defective expression of H and M proteins was not due to a restriction in the transcription of their mRNAs. In contrast, the mRNA for P protein, the most abundant MV mRNA in these lytically infected T lymphoid cells, is markedly underexpressed in the homologous p.i. Thus the underexpression of P protein in p.i. could be due to a decreased availability of P mRNA. This unbalanced underexpression of MV proteins may impair the cell fusion and c.p.e. of MV and facilitate viral persistence in human lymphoid cells.