Processing of Donor DNA during Haemophilus influenzae Transformation: Analysis Using a Model Plasmid System

A plasmid system was used to investigate the processing of donor DNA during transformation of competent Haemophilus influenzae. Using biochemical and genetic methods, we have determined that portion of a donor plasmid molecule that, on average, can become integrated into a homologous recipient plasmid during transformation. Our results show that (i) transformation efficiency decreases linearly with donor DNA length over the range of 11 to 3.5 kilobase pairs, (ii) transformation efficiency decreases exponentially with size for donor molecules less than 3.5 kilobase pairs in length, and (iii) 5′-end label, but not 3′-end label, can be specifically incorporated into the resident homologous region. We present a model for donor processing during entry that encompasses and explains these observations.