Electron microscopy of single-stranded structures in the DNA of competent Haemophilus influenzae cells.
Chromosomal DNAs from exponential-phase and competent cells of Haemophilus influenzae were examined by electron microscopy to determine whether the chromosome undergoes structural changes during competence development. Single-stranded gaps and single-stranded tails formed in chromosomal DNA during competence development. The generation of gaps was dependent on the rec-2 function. Since the rec-2 mutant is defective in the translocation of donor DNA, it was inferred that the gaps were involved in the translocation step of transformation. The generation of single-stranded tails was independent of the rec-1 and rec-2 genes. Therefore, these structures were assumed to play no direct role in the interaction of donor and recipient DNAs during transformation. Gaps were preferentially associated with a readily denaturable, possibly A + T-rich fraction of the genome. This finding raised the possibility that hot spots for transformation might be associated with A + T-rich DNA.
D002876:Chromosomes, Bacterial / Q000032:analysis; D004269:DNA, Bacterial / Q000648:ultrastructure*; D004277:DNA, Single-Stranded / Q000648:ultrastructure*; D006193:Haemophilus influenzae / Q000032:analysis*; D008854:Microscopy, Electron; D009691:Nucleic Acid Denaturation
D004269:DNA, Bacterial; D004277:DNA, Single-Stranded