Disruption of norA in A. flavus AF13. (A) Schematic showing design of the knockout vector. Numbers denote the position of the region in AF13 DNA (Genbank accession number AY51051). P1 to P4 are the oligonucleotides primers used for amplification of the 5’- and 3’-ends of the gene. The neighboring genes estA and ver-1 are shown. niaD was obtained from an XbaI digest of pSL82. The construct was prepared in pUC18. (B) PCR with oligonucleotide primers P1 and P4 of AF13 DNA from different transformant clones. Lane 1, 1 kb+ marker (Invitrogen); Lane 2, AF13 (pSL82) control; Lanes 3–5, AF13ΔnorA-clones 3, 15, 21, respectively.