Conjugation in single strand DNA transfer of E. coli cells, use special fluorescent antibodies during the cross in Hfr and F- strain.
• The parental Hfr strains are black with red DNA. The red is from the binding of an antibody to a protein normally attached to DNA.
• The recipient F-cells are green due to the presence of the gene, for a jellyfish protein that fluoresces green because they are mutant, for a certain gene. Their DNA protein does not bind to the antibody.
• When single stranded DNA enters the recipient, it promotes binding of the protein, which fluoresces yellow in the back ground. This shows Hfr’s and ex-conjugants have undergone conjugation with yellow transferred DNA.
Thus, the yellow spots represent the DNA of F‾ recipients that have taken up DNA from the Hfr donor strain. The yellow spots are ex-conjugants, the cells that have undergone conjugation. When single-stranded DNA enters the recipient, it promotes atypical binding of DNA protein, which fluoresces yellow.