Three new dominant C1 suppressor alleles in Zea mays

Three new dominant suppressor mutations of the C1 transcription regulator gene in maize - C1 - I Delta 1, C1-I Delta 2 and CI-I Delta 3 - are described that suppress anthocyanin colouration in kernels similar to the function of the C1-I standard inhibitor. The C1-I Delta mutations were induced by imprecise excision of an En/Spm transposon in the third exon of the C1 gene. These transposon footprints cause a frameshift in the C1 open reading frame that leads to truncated proteins due to an early stop codon 30 amino acids upstream of the wild-type C1 protein. Therefore, the C1-1 Delta gene products lack the carboxy-terminal transcriptional activation domain of C1. The C1-I standard allele also lacks this domain and in addition differs in 17 amino acids from the wild-type C1 allele. The new C1-I Delta alleles provide evidence that deletion of the carboxy-terminal activation domain alone is sufficient to generate a dominant suppressive effect on the function of wild-type CI.