M13 Phage: Introduction

M13 (or f1) phages are filamentous phages that infect E. coli through pili, and are able to produce new virions without lysing the host cell.  M13 has some key structural elements:

  • Circular, single-stranded DNA
  • ~6.4 kb long
  • 10 genes in the genome.

Of these 10 genes, we are concerned with the following three:

  • Gene II: codes for nickase, allows rolling-circle replication
  • Gene III: codes for the pilot protein, which guides the nascent ssDNA to the membrane,
  • Gene VIII: coat protein, encapsulates the pilot protein and the ssDNA phage DNA as it extrudes through the membrane

M13 phages are useful for a number of applications:

  • sequencing
  • mutagenesis
  • probes
  • lambda-ZAP subcloning
  • phage display libraries