Molecular characterization of the α-amylase genes of Lactobacillus plantarum A6 and Lactobacillus amylovorus reveals an unusual 3′ end structure with direct tandem repeats and suggests a common evolutionary origin

Abstract The α -amylase gene (amy A) of Lactobacillus plantarum A6 was isolated from the genome by polymerase chain reaction with degenerated oligonucleotides, synthesized according to the tryptic peptide amino acid sequences of the purified enzyme. Nucleic acid sequence analysis revealed one open reading frame of 2739 bp encoding a 913 amino acid protein. The amylase appears to be divided into two equal parts. The N-terminal part has the typical characteristics of the well-known α -amylase family (65% identity with the α -amylase of Bacillus subtilis and 97% identity with the partial sequence available for the α -amylase of Lactobacillus amylovorus ). The C-terminal part displays a fairly unusual structure. It consists of four direct tandem repeated sequences of 104 amino acids sharing 100% similarity. The complete nucleotide sequence of the α -amylase gene of L. amylovorus was also determined. An open reading frame of 2862 bp encoding a 954 amino acid protein was identified. Perfect homology between the two amy A genes was observed in the N-terminal region. The C-terminal part of L. amylovorus α -amylase also included tandem repeat units but striking differences were observed: (i) the addition of one repeat unit; (ii) a shorter, 91 amino acid repetition unit. These structural homologies suggest that both genes have a common ancestor and may have evolved independently by duplication with subsequent recombination and mutation.