Triparental mating was then performed . as a result , we obtained 91 recombined plasmids , 23 possible single - cross mutants and 53 possible double - cross mutants . pcr analysis of the genomic dna from the resulting possible double - cross mutants indicated that 6 of them were wild - type , 4 of them were single - cross mutants and the remainder ones were true double - cross mutants
