Figure 5.

Southern blots of genomic DNA from the parent Volvox strain, 153–48, and from transformants HRN-1, HRN-2, and HRN-3. The sizes of DNA standards are indicated on the left, and hybridizing bands (arrowheads) are indicated on the right. DNA was digested with EcoRI or SalI, and the blot was probed with an ≈0.3-kb EcoRI/ApaI nitrate reductase fragment. The probe covers the nitA gene region upstream of the 5′ end of the nitA sequence present in the replacement vector used for the Southern blot experiments and, therefore, excludes signals resulting from sites of illegitimate plasmid integration. An 8.8-kb (EcoRI) fragment and a 3.0-kb (SalI) fragment were predicted if the homologous recombination event did not affect the immediate surroundings at the 5′ end or at the 3′ end of the nitA gene. E, EcoRI; S, SalI.