Genetic and molecular events in transformation of Haemophilus influenzae with plasmid RSF 0885 carrying cloned segments of chromosomal DNA

Abstract

In Haemophilus influenzae genetic transformation for a plasmid marker is significantly increased when recombinant plasmid RSF 0885 DNA carrying chromosomal DNA segments is used instead of the plasmid DNA alone. Chromosomal DNA by itself, added even a few minutes after the addition of plasmid DNA to competent cells, stopped further uptake of the plasmid DNA. These observations are consistent with the idea that plasmid RSF 0885 contains a 'degenerate' version of the required eleven base-pair 'uptake sequence'inHaemophilus. The transformation activity of the recombinant plasmid DNA is recoverable after its entry into cells, although the specific biological activity of the re-isolated plasmid DNA is less than that of the parental recombinant plasmid DNA. The rec 1 gene function of the host is necessary for obtaining higher transformation frequencies with recombinant DNA from five different clones. The reduced transformation frequencies seen inrec 1^- strain is not all due to a permanent damage to the donor DNA since the recovered recombinant plasmid DNA from such cells can increase the transformation efficiency on rec 1⁺ strain.