Bacteriophage λ based vector-Bacteriophage are the viruses using bacteria as their host for replication. Bacteriophage λ is the virus of E.coli and have been used to develop vector for genetic engineering. Before discussing properties of bacteriophage λ based vector, it is important to understand bacteriophage biology.

Bacteriophage λ genome- Phage genome is a linear double stranded DNA of 48.5kb (Figure 18.1). On both end of the genome, it has a stretch of 12 nucleotides which are complementary to each other. These sites are known as “cos sites” and it allows circularization of virus genome after entering into the host cell. Genes are arranged in between these two cohesive ends and codes for proteins responsible for making head, tail, factor for recombination and process of lysogeny. The central region of the genome is non-essential and can be replaced without much affecting growth and infectivity of the virus. As a result this region can be exploited to develop cloning vector with multiple approaches as discussed later in the lecture.

Figure 18.1: Map of bacteriophage λ chromosome.