Structure of a gene encoding the 1.7 S storage protein, napin, from Brassica napus

A rapeseed chromosomal region containing a gene (napA), which encodes the 1.7 S seed storage protein (napin), was isolated in several overlapping recombinant clones from a phage lambda genomic library. Following restriction enzyme mapping of the genomic region, a subclone containing the napA coding region as well as some 1.1 and 1.4 kilobases of DNA from the 5' and 3' regions, respectively, was mapped and sequenced. The gene turned out to lack introns. Southern blotting analyses utilizing a napin cDNA clone as a probe revealed the presence of on the order of 10 napin genes in the rapeseed genome. The major polyadenylated transcript encoded by these genes was shown to be an 850-nucleotide species, the initiation site of which was mapped onto the napA gene. The major initiation site for transcription is located some 33 nucleotides downstream from a sequence perfectly conforming to the consensus sequence of a TATA box. Further analyses of the sequence revealed several features that may be of relevance for the expression of the napin genes.