Episomes

Epissomes are a genetical component that can either live freely and independently in the bacterial cytoplasm (having several copies in that environment) or be inserted in the main bacterial chromosome, thus, replicating with it. In other words, it is an equivalent of bacterial plasmids. In fact, plasmids are an example of this genetic element.

 In general, episomes are closed circular DNA molecules that are replicated in the nucleus of the host cell. Viruses are the most common examples of this (for example, viruses that perform the lysogenic cycle).