Altered 3'-terminal RNA structure in phage Qβ adapted to host factor-less Escherichia coli

摘要

The RNA phage Qβ requires for the replica- tion of its genome an RNA binding protein called Qβ host factor or Hfq protein. Our previous results suggested that this protein mediates the access of replicase to the 3'-end of the Qβ plus strand RNA. Here we report the results of an evolutionary experiment in which phage Qβ was adapted to an Escherichia coli Q13 host strain with an inactivated host factor (hfq) gene. This strain initially produced phage at a titer ≈10,000-fold lower than the wild-type strain and with minute plaque morphology, but after 12 growth cycles, phage titer and plaque size had evolved to levels near those of the wild-type host.