M13 is a bacteriophage, a virus that infects bacteria. It consists of a protein capsid containing circular single-strand DNA. The DNA is comprised of 6407 nucleotides. The protein capsid is formed from a couple thousand copies of a 50-amino-acid protein called P8. M13 infects the E. Coli bacteria and is of significant interest and use in research utilizing recombinant DNA and phage displays.
Pair Potential of Charged Colloidal Stars. F. Huang, K. Addas, A. Ward, N.T. Flynn, E. Velasco, M.F. Hagan, Z. Dogic, and S. Fraden, Physical Review Letters 102, 108302 (2009).