At the core is the a circular, single-stranded DNA genome arranged in a linear shape. (imagine grabbing a rubber band at both ends and stretching it out so that it is a very elongated and narrow oval) There are 5 types of coat proteins that then coat and protect this DNA. here is a link to a decent site about M13: <a href="http://www.biosci.ohio-state.edu/~mgonzalez/Micro5">http://www.biosci.ohio-state.edu/~mgonzalez/Micro5</a> 21/Lambda/M13.html [ohio-state.edu]