[Structure of the recombination zone during abnormal excision of the transducing bacteriophage lambda plac9].

Investigating molecular mechanism of illegitimate recombinations in prokaryote we study transducing bacteriophages of the lambda lac series. We have carried out physical mapping of bacteriophage lambda plac9 DNA and, by comparing the obtained results with the data on the structure of lambda DNA and lac operon of E. coli, located the phage-bacterial junction corresponding to the lambda-lac9 abnormal excision and elucidated the nucleotide sequence around the junction. It led to the primary structure of phage and bacterial segments in the lysogenic bacterium which took part in the recombinational act leading to the abnormal excision and lambda lac9 formation. Structural homology of the partners in the lambda plac9 excision proved to be lower than in case of the earlier studied lambda plac5 and lambda plac10 whose excision proceeded regioselectively. Various aspects of the crossover area, including the crossover point's probable position and enzymic systems participating in the abnormal excision, are discussed.