Aleurain: a barley thiol protease closely related to mammalian cathepsin H.

We have isolated and sequenced a 1400-base-pair cDNA derived from gibberellic acid-treated aleurone cell mRNA. This sequence contains an open reading frame that would code for a protein of 361 amino acids. The carboxyl-terminal two-thirds of the predicted amino acid sequence is closely related to that of the rat lysosomal thiol protease cathepsin H; the initial 143 amino acids may code for a secretory peptide plus a prosegment. The expression of this aleurone thiol protease mRNA is unusual in that, in aleurone cells, its abundance is regulated by the plant hormones gibberellic acid and abscisic acid, but it is also expressed at high levels in leaf and root tissue. This protease may represent the equivalent of a plant lysosomal thiol protease.