Lambda phage

The lambda phage is a model organism studied in biology laboratories.

Classification of the lambda phage

The lambda phage is a virus which belongs to the Siphoviridaefamily. It infects the bacterium which is widely used in the laboratory, Escherichia coli.

Characteristics of the lambda phage

The lambda phage has a 48,500 base pair, linear, double-stranded DNA genome which has been entirely sequenced. It has the typical shape of a bacteriophage, a head in which the DNA is encapsulated and a tail and fibrils which enable it to attach itself and insert its DNA into the cell.

It can be involved in two different cycles:

• the lytic cycle, in which the infected bacterium dies and releases a large number of new virions, synthesised as a result of expression of the viral genes, which particularly leads to the production of capsid proteins ;
• the lysogen cycle, in which the viral genome is incorporated into the bacterial genome (as a prophage) and where the latency genes are expressed.

Use of the lambda phage in the laboratory

The lambda phage is studied to improve our understanding of host-virus relationships and also as a cloning vector.