Cytomegalovirus (CMV) is a particular threat to individuals with a suppressed immune system, such as transplant patients or people infected with the Human Immunodeficiency Virus (HIV). It is also responsible for causing severe abnormalities in the unborn child if the mother is infected during pregnancy, leading to deafness, visual impairment and sometimes brain damage.

Symptoms of infection are sore throat, fever and occasionally mild hepatitis (liver disease). After infection the virus stays in the body for life in a dormant state called latency. It is estimated that up to 80% of the population are latently infected with CMV. When the immune system is weakened the virus is able to reactivate and cause new and often more severe disease symptoms.

To understand how a virus works scientists can modify its genes in the laboratory. Experiments can then be performed to study the effects on the virus. These changes can be detected in virus-infected cells by adding chemicals that cause them to change colour if the modified gene is expressed (switched on).

Cytomegalovirus contains a protein called pp71, which switches genes on during the early stages of virus infection. In this experiment modifications were made to pp71, to try and identify important parts of the protein responsible for switching viral genes on.