INTRON-DEPENDENT TRANSIENT EXPRESSION OF THE MAIZE GAPA1 GENE

Transient expression experiments show that the maize GapAl promoter ex hibits a requirement for sequences contained within intron 1 and surro unding exon border regions for expression in maize Black Mexican Sweet cells. Maize GapA1-promoter constructs lacking intron 1 are inactive. Intron 1 and its exon border sequences, when reintroduced into constr ucts lacking introns, restore gene activity whereas intron 2 and its e xon borders to not. The minimal promoter so defined encompasses roughl y 250 bp upstream of the in vivo transcription start and appears also to include intron 1. An octameric sequence was identified in intron 1 of maize GapA1 which is similar to sequence motifs found in other maiz e introns known to increase transient expression. Partial restoration of gene expression in GapA1 constructs lacking intron 1 was achieved t hrough insertion of the identified octameric sequence.