Differential expression of Ustilago maydis DNA sequences during induction of nitrate reductase enzyme activity.

A differential hybridisation screen of an Ustilago maydis genomic DNA library was used to identify DNA sequences transcribed at higher levels under growth conditions which induce nitrate reductase activity. After two rounds of screening, four different sequences showed a strongly enhanced hybridisation signal with an induced cDNA probe relative to a repressed cDNA probe. The sequence in plasmid pMH3007 hybridised to a U. maydis RNA transcript of a 4.2 kb. This is identical in size to a transcript, also nitrate inducible, which hybridised to cloned Aspergillus nidulans nitrate reductase gene sequences at a reduced stringency.