MOLECULAR CHARACTERIZATION OF THE ALPHA-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

The alpha-amylase gene (amyA) of Lactobacillus plantarum A6 was isolat ed from the genome by polymerase chain reaction with degenerated oligo nucleotides, synthesized according to the tryptic peptide amino acid s equences of the purified enzyme. Nucleic acid sequence analysis reveal ed 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-termin al part has the typical characteristics of the well-known alpha-amylas e family (65% identity with the alpha-amylase of Bacillus subtilis and 97% identity with the partial sequence available for the alpha-amylas e of Lactobacillus amylovorus). The C-terminal part displays a fairly unusual structure. It consists of four direct tandem repeated sequence s of 104 amino acids sharing 100% similarity. The complete nucleotide sequence of the alpha-amylase gene of L. amylovorus was also determine d. An open reading frame of 2862 bp encoding a 954 amino acid protein was identified. Perfect homology between the two amyA genes was observ ed in the N-terminal region. The C-terminal part of L. amylovorus alph a-amylase also included tandem repeat units but striking differences w ere observed: (i) the addition of one repeat unit; (ii) a shorter, 91 amino acid repetition unit. These structural homologies suggest that b oth genes have a common ancestor and may have evolved independently by duplication with subsequent recombination and mutation. (C) 1997 Else vier Science B.V.