Rice is one of the plant species most tolerant to anaerobic condition and can germinate in complete absence of oxygen. The expression of transcription factors is therefore likely to play an important role in determining the kind of response to environmental stress. We report the isolation of a rice cDNA clone encoding a myb factor, myb7, expressed during anoxia. The myb conserved domain consists of imperfect repeats of 50-53 amino acids, known as 'tryptophan cluster', because of high conserved tryptophan residues involved in stabilising the structure of DNA binding domain. One positive clone, myb7, was isolated.
Some peculiar features suggesting post-transcriptional regulation are present.
The putative polypeptide encoded by the uORF is 40 amino acids long and is rich in leucin and arginine residues. Most eucaryotic mRNA encode a single polypeptide, starting at the first AUG codon and the introduction of AUG codons in the mRNA leader, strongly reduces the expression of downstream coding sequences. However PCR analysis with specific oligonucleotides, revealed the presence in anaerobically grown coleoptiles of mRNA corresponding to both spliced and unspliced myb7 transcript in an almost equimolar quota. The high amount of unspliced myb7 RNA in respect to spliced form suggests that post-transcriptional regulation rather than a trivial escape is acting. The observation that the 5' region of the intron could direct the synthesis of a in-frame short leucin zipper supports the idea of a regulatory role for myb7 splicing.