Semliki Forest virus replication complex capable of synthesizing 42S and 26S nascent RNA chains

A complex synthesizing Semliki Forest virus (SFV)-specific RNAs was purified from infected HeLa cells. During purification, the RNA-synthesizing complex was monitored by the presence of RNA chains synthesized during a 1 min pulse in vivo and the ability to synthesize 42S and 26S RNAs in vitro. Finally, the protein composition of the replication complex was analysed. Thirty to 40% of the pulse-labelled RNAs and 10 to 25% of the polymerase activity present in the postnuclear supernatant were recovered in smooth membranes. At this stage of purification single stranded 42S and 26S RNA were synthesized and released from the replication complex in vitro. After treatment of the smooth membrane fraction with Triton X-100 the replication complex was solubilized. When analysed by sucrose gradient centrifugation, the solubilized replication complex distributed heterogeneously. It had reduced RNA polymerase activity, but was still able to synthesize both 42S and 26S nascent RNA chains which were not released from RIs and RFs. The non-structural protein ns70 was the major virus-specified component associated with the replication complex.