ROLES OF THE INFLUENZA-VIRUS POLYMERASE AND NUCLEOPROTEIN IN FORMING A FUNCTIONAL RNP STRUCTURE

Influenza virus transcription and replication is performed by ribonucl eoprotein particles (RNPs). They consist of an RNA molecule covered wi th many copies of nucleoprotein (NP) and carry a trimeric RNA polymera se complex, RNA modification analysis and electron microscopy performe d on native RNPs suggest that the polymerase forms a complex with both conserved viral RNA (vRNA) ends, whereas NP binding exposes the RNA b ases to the solvent. After chemical removal of the polymerase, the bas es at the vRNA extremities become reactive to modification and the vRN Ps behave as structures with free ends, as judged from the observation of salt-induced conformational changes by electron microscopy. The vR NA appears to be completely single-stranded in polymerase-free RNPs de spite a partial, inverted complementarity of the vRNA ends. The absenc e of a stable double-stranded panhandle structure in polymerase-free R NPs has important implications for the mechanism of viral transcriptio n and the switch from transcription to replication.