Abstract
The amylose-extender (Ae) gene encoding starch-branching enzyme IIb (SBEIIb) in maize is predominantly expressed in endosperm and embryos during kernel development. A maize genomic DNA fragment (−2964 to +20 485) containing the Ae gene was isolated and sequenced. The maize Ae mRNA is derived from 22 exons distributed over 16 914 bp. Twenty-one introns, differing in length from 76 bp to 4020 bp, all have conserved junction sequences (GT⋅⋅AG). Sequence analysis of the 5′- and 3′-flanking regions revealed a consensus TATA-box sequence located 28 bp upstream of the transcription initiation site as determined by primer extension analysis, and a putative polyadenylation signal observed 29 bp upstream of the polyadenylation site based on cDNA sequence. Genomic Southern blot analysis suggests that a single Ae gene is present in the maize genome. Promoter activity was confirmed by testing a transcriptional fusion of the Ae 5′-flanking region between −2964 and +100 to a luciferase reporter gene in a transient expression assay using maize endosperm suspension cultured cells. 5′ deletion analysis revealed that the 111 bp region from −160 to −50 is essential for high-level promoter activity.