Autolysis and natural competence contribute to the ability of Neisseria to undergo antigenic variation, an important virulence factor that allows it to avoid an effective immune response by the host...

Autolysis and natural competence contribute to the ability of Neisseria to undergo antigenic variation, an important virulence factor that allows it to avoid an effective immune response by the host and that also contributes to cell and tissue tropism. To determine the importance of RecA-dependent recombination in antigenic variation in Neisseria, you make a mutant of Neisseria lacking the recA gene and you develop a PCR method for detecting whether homologous recombination has occurred. The method you develop involves using a primer to the N-terminal region of the pilE gene and a set of primers to the C-terminal regions of several of the pilS genes. You find that the PCR using these primers yields a product for the wild-type Neisseria strain, but not for the

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recA mutant strain. You conclude that RecA-dependent recombination is important for antigenic variation to occur. Explain what is the basis of the experimental design that allowed you to come to this conclusion (i.e., how could you tell whether antigenic variation occurred using this PCR method?).