Figure 22.4: Insertional Inactivation of LacZ gene to screen recombinant clone.

(3) Insertional Inactivation of cI gene- During an infection cycle, virus undergoes a lytic and lysogenic stages. The lytic phase is responsible for lysis of host to release the virus particle where as lysogenic stage allow the replication of virus without lysis of host. The cI gene encodes for cI repressor and which is responsible for the formation of lysogens. In the presence of functional cI, the plaques contains unlysed host cells and has a turbid appearance where as in the absence it will clear. This feature can be use to screen the clone to detect functional cI (absence of clone) or absence of cI (presence of insert). This approach is schematically depicted in Figure 22.5.