Temperate bacteriophage 186 is a tailed P2-like virus in the myoviridae family which infects the bacterial host Escherichia coli. Following infection, 186 can enter one of two distinct but interchangeable life cycles in the host, lysis or lysogeny. In the lysogenic state, the virus integrates into the host genome forming a prophage. Following host DNA damage through, for example, UV irradiation, viral replication and viral particle synthesis is induced, culminating in lysis of the host cell and release of mature virus particles. The lysogenic state is maintained by a DNA looping oligomeric transcription factor, cI, comprising two domains, a DNA binding domain and an oligomerisation domain. An X-ray crystal structure of the oligomerisation domain inferred the formation of a wheel-like structure comprising a heptamer of dimers [1]. Recent native mass spectrometry evidence suggests the complex forms a dodecamer in solution. To resolve this ambiguity, and to understand the complex mechanism of transcriptional regulation orchestrated by 186 cI, we aim to determine the structure of the DNA bound oligomer by cryo-EM. Additionally, no complete P2-like virus virion structures have been determined. We aim to determine the composition, stoichiometry and structure of the 186 virus particle by a combined cryo-EM and native mass spectrometry approach. Structural evidence will permit rational design of novel virion functionality, for example in engineering enhanced antimicrobial activity and development of a protein chassis for targeted delivery of therapeutics.