In DNA cloning ,a given DNA fragment is inserted into an autonomously replicaating DNA molecule ,called a cloning vector, so that the inserted DNA is replicated with the vector.A number of diffferent viruses have been used as vectors,including bacterial viruses,insect viruses,and mammalian retroviruses.Acommon bacterial virus used as a vector is Bacteriophage Lambda.if a gene is inserted into bacteriophage lambda and the resulting recombinanat lambda phage is used to infect E.colli,the inserted gene will be expressed by the bacteria.