Index >> Bacterial Recombination >> Specialzied Restricted Genetic Transduction

All the gal+ transductants were found to be actively lysogenic (i. e. capable of liberating infective lambda phages on induction), or at least had immunity to infection from exogenous lambda. Most of the gal+ mutants were also found to be genetically unstable. About 1-10% of the individuals lost the gal + character and reverted to the gar phenotype.

When the lambda chromosome enters the bacterial host cells it either enters the lytic cycle, or is incorporated into the E. coli chromosome by recombination, and becomes a prophage. In the latter case the host survives integration and becomes a lysogen. In the lytic cycle the phage chromosome replicates and produces about a hundred progeny.

The transduced genes are linked to the viral chromosome. Normal excision takes place in the vast majority of cells, giving rise to a circular viral chromosome and a nonlysogenic bacterial chromosome. The viral chromosome replicates by the rolling circle mechanism and produces several copies. Each unit length DNA is then packaged into infectious particles. When abnormal excision takes place (1 cell out of 100,000), a circular molecule containing some host DNA is formed. When this replicates, it gives rise to infectious particles containing a segment of bacterial DNA which has replaced a segment of viral DNA. Depending upon the site of abnormal excision, different virus variants are formed