Isolation of free minus strands from Qβ-infected Escherichia coli

Free minus strands (minus strands not involved in a firm duplex structure) are produced in Escherichia coli infected with the RNA phage Q_β. These minus strands can be extracted from the cells under conditions of mild lysis and low salt concentrations, and can be purified by electrophoresis on polyacrylamide gels.The free minus strands are fully competent as template for the Q_β-replicase in the absence of host factors, directing the synthesis of plus strands.