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’ in Haemophilus. 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 in rec 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.