MOLECULAR HETEROGENEITY OF SMALL-SUBUNIT ADPGLUCOSE PYROPHOSPHORYLASECDNAS ISOLATED FROM TUBEROUS ROOTS OF SWEET-POTATOES

Four cDNAs (sT1, sT2, sT3 and sT4) encoding the small subunit of ADPgl ucose pyrophosphorylase (AGPase) were isolated fi om sweet potato tube rous roots. These cDNAs showed heterogeneity in nucleotide and amino a cid sequences. In the protein coding sequences they showed a very high identity (>99%). But the sequences diverged in the 3'UTRs of sT1 and sT2. The size of 3'UTRs were various in sT1, sT3 and sT4. The comparis on of sT1 with a previously identified small subunit AGPase cDNA of sw eet potatoes (SAPS) showed 91% identity at the nucleotide level and 96 % identity at the amino acid level. Genomic southern analysis revealed that the small subunit AGPase polypeptide was encoded by multi-copy g enes, suggesting the possibility that four isoforms originate from a d ifferent locus of sweet potato genome. With the level of nucleotide se quence conservation, the possible roles of various isoforms are discus sed. The possible subgroups of isoforms are also discussed in terms of the level of nucleotide sequence conservation.