Specificity of insertion of Tn1545 transposon family in Lactococcus lactis subsp. lactis

A collection of Lactococcus lactis subsp. lactis strains carrying a derivative of Tn1545 inserted in the chromosome was generated. Some 34 insertions were cloned in Escherichia coli and the flanking DNA sequences determined. Insertions are distributed non randomly and several hot spots were observed. The hot spots do not have sequence features which would distinguish them from other insertion sites, suggesting that they may have special structural properties. Insertions in open reading frames occurred at a far lower frequency than expected for random transposition and were most often located near potential terminator and promoter sequences. Different mutations in the extremities of the transposon do not affect the specificity of insertion. We suggest that target specificity is mainly due to the properties of the intergrase itself.