Q beta replicase is a unique RNA polymerase complex, comprising Q beta virus-encoded RNA-dependent RNA polymerase (the catalytic beta-subunit) and three host-derived factors: translational elongation factor (EF) -Tu, EF-Ts and ribosomal protein S1. For almost fifty years, since the isolation of Q beta replicase, there have been several unsolved, important questions about the mechanism of RNA polymerization by Q beta replicase. Especially, the detailed functions of the host factors, EF-Tu, EF-Ts, and S1, in Q beta-replicase, which are all essential in the Escherichia coli (E. coli) host for protein synthesis, had remained enigmatic, due to the absence of structural information about Q beta replicase. In the last five years, the crystal structures of the core Q beta replicase, consisting of the beta-subunit, EF-Tu and Ts, and those of the core Q beta replicase representing RNA polymerization, have been reported. Recently, the structure of Q beta replicase comprising the beta-subunit, EF-Tu, EF-Ts and the N-terminal half of S1, which is capable of initiating Q beta RNA replication, has also been reported. In this review, based on the structures of Q beta replicase, we describe our current understanding of the alternative functions of the host translational elongation factors and ribosomal protein S1 in Q beta replicase as replication factors, beyond their established functions in protein synthesis.