Genes coding for the major tuberous root protein of sweet potato: Identification of putative regulatory sequence in the 5' upstream region.

The isolation and characterization is described of sporamin A and B genes, gSPO-A1 and gSPO-B1, respectively, which are members of two distinct subfamilies of the multigene family encoding the major soluble protein of sweet potato tuberous root. The nucleotide sequences of the two genes along with the 5' and 3' flanking regions were determined. The transcriptional start sites were determined by S1 nuclease mapping. Comparison of the sequences with those of the full-length cDNAs for sporamin A and B reveals that these genes contain no introns. Sequence comparison by dot matrix plot analysis shows that homology of the 5' flanking regions between gSPO-A1 and gSPO-B1 extends only to 45 bp upstream of the transcription start site, which includes the consensus TATA box sequence. The sequence of this region is also conserved in the sporamin-related gene, gSPO-X1, which dose not seem to be expressed in the tuberous root. The sequences further upstream diverge extensively, but two short sequence blocks of 28 to 29 bp and 19 to 22 bp are found in the 5' flanking sequence of gSPO-A1 and gSPO-B1 but not in gSPO-X1. The 19-22 bp sequence block is repeated twice in gSPO-A1 and four times in gSPO-B1. These conserved sequence blocks may play regulatory roles in their expression.