Directed deletions in the aflatoxin biosynthesis gene homolog cluster of Aspergillus oryzae

To investigate the structure of the aflatoxin gene cluster in Aspergillus o ryzae, 39 strains belonging to this species were examined for the existence of pksA, fas1A, aflR and vbs, and the results compared with those for ver- 1 obtained previously. These five genes are involved in aflatoxin biosynthe sis in Aspergillus parasiticus. The strains examined were categorized into three groups: group 1, having the five homologs, 2, having ver-1 and vbs: a nd 3, having vbs homologs. Long-PCR analysis of the regions between the fiv e homologs in A. oryzae IFO 4135, coupled with Southern-hybridization analy sis, shows that those homologs are clustered with the same arrangement as i n A. parasiticus. These results suggest that directed deletions of the clus ter occur in A. oryzae strains. The possible breakpoints of the deletions i n the strains of group 2 and 3 were estimated.