What is a prophage?

A prophage is indeed accurately defined as a dormant state of a bacteriophage integrated into bacterial chromosomes. In this state, the viral DNA is incorporated into the bacterial genome and can replicate along with it when the bacterial cell divides. This integration can be a crucial part of the life cycle of bacteriophages, particularly those that undergo lysogenic cycles, as it allows the viral genetic material to be passed on to subsequent generations of bacterial cells.

When conditions become favorable, the prophage can be induced to enter the lytic cycle, where it becomes active, leading to the production of new viral particles and eventual lysis of the bacterial cell. This interplay between the prophage and the bacterial host is a key aspect of viral ecology and bacteriophage capabilities.

The other options provided do not capture the specific characteristics of a prophage. For instance, an active virus infecting a bacterial cell represents a different stage in the viral life cycle. A sequence of DNA coding for a protein is a broader definition of a gene, while an enzyme that synthesizes DNA from RNA templates refers to reverse transcriptase, which is unrelated to the concept of a prophage.