A novel wheat α-amylase gene (α-Amy3)

Summary

A genomic clone of a wheat α-amylase gene (λAmy3/33) was identified, on the basis of hybridisation properties, as different from α-Amy1 and α-Amy2 genes which had been characterised previously. The nucleotide sequence revealed that this gene has the normal sequence motifs of an active gene and an open reading frame interrupted by two introns. The protein sequence encoded by this open reading frame is recognisably similar to that of α-amylase from the α-Amy1 and α-Amy2 genes and there is high sequence homology in all three proteins at the putative active sites and Ca⁺⁺ binding region. In addition, the introns are at positions equivalent to the position of introns in the α-Amy1 and α-Amy2 genes. However, the sequence was less similar to α-Amy1 and α-Amy2 than these are to each other. Southern blot analysis showed that the λAmy3/33 DNA is one of a small multigene family carried on a different chromosome (group 5) from either the α-Amy1 or α-Amy2 genes. A further difference from the α-Amy1 and α-Amy2 genes was the pattern of expression. λAmy3/33 was expressed only in immature grains and, unlike the α-Amy1 and α-Amy2 genes, not at all in germinating aleurones. These data suggested therefore that this gene represents a third type of α-amylase gene, not described before, which shares a common evolutionary ancestor with the α-Amy1 and α-Amy2 genes.