Characterization of a Maize β-Amylase cDNA Clone and Its Expression during Seed Germination

A maize (Zea mays L.) cDNA clone (pZMB2) encoding β-amylase was isolated from a cDNA library prepared from the aleurone RNA of germinating kernels. The cDNA encodes a predicted product of 488 amino acids with significant similarity to known β-amylases from barley (Hordeum vulgare), rye (Secale cereale), and rice (Oryza sativa). Glycine-rich repeats found in the carboxyl terminus of the endosperm-specific β-amylase of barley and rye are absent from the maize gene product. The N-terminal sequence of the first 20 amino acids of a β-amylase peptide derived from purified protein is identical to the 5th through 24th amino acids of the predicted cDNA product, indicating the absence of a conventional signal peptide in the maize protein. Recombinant inbred mapping data indicate that the cDNA clone is single-copy gene that maps to chromosome 7L at position 83 centimorgans. Northern blot analysis and in vitro translation-immunoprecipitation data indicate that the maize β-amylase is synthesized de novo in the aleurone cells but not in the scutellum during seed germination.