REGULATED EXPRESSION OF THE NOR-1 AND VER-1 GENES ASSOCIATED WITH AFLATOXIN BIOSYNTHESIS

RNA transcript accumulation for the ver-1 and nor-1 genes, which are a ssociated with aflatoxin biosynthesis in the fungus Aspergillus parasi ticus, was measured before and during aflatoxin production in liquid s hake culture. Transcripts were not detected until near the end of trop hophase (growth phase) and could still be observed well into stationar y phase during batch fermentation in an aflatoxin-supporting growth me dium. Maximum accumulation of both transcripts occurred just prior to the onset of stationary phase. Aflatoxin B, was first detected approxi mately 8 h after the appearance of the ver-1 and nor-1 transcripts. In contrast, maximum transcript accumulation for the pyrG gene (encoding orotidine monophosphate decarboxylase), which is involved in primary metabolism, was observed at the onset of trophophase when the ver-1 an d nor-1 transcripts could not be detected. Accumulation of the ver-1 a nd nor-1 transcripts was also studied following a nutritional shift fr om a non-aflatoxin-supporting medium (peptone mineral salts [PMS]) to a glucose-containing medium (glucose mineral salts [GMS]), which does support aflatoxin biosynthesis. Transcripts from ver-1 and nor-1 could not be detected on PMS medium but did accumulate approximately 4 to 7 h following transfer to GMS medium. Additionally, aflatoxins were not detected in PMS medium but were observed to accumulate within 24 h af ter the shift from PMS to GMS. These data suggest that aflatoxin biosy nthesis is in part regulated by the accumulation of the ver-1 and nor- 1 transcripts.