A plant serpin gene

Abstract

A 3133‐bp nucleotide sequence of the gene Paz 1 on chromosome 4 of barley, encoding endosperm protein Z 4 , has been determined. The sequence includes 1079 bp 5′ upstream and 523 bp 3′ downstream of the coding region. The 1079‐bp 5′ upstream region of the gene shows little similarity to 5′ regions of other sequenced genes expressed in the developing cereal endosperm. The coding sequence is interrupted by one 334‐bp‐long intron (bases 1497–1830). The deduced amino acid sequence, which was corroborated by peptide sequences, consists of 399 amino acids and has a molecular mass of 43128 Da. This sequence confirms protein Z 4 to be a member of the serpin superfamily of proteins. The similarity with other members of the family expressed as amino acids in identical positions is in the order of 25–30% and pronounced in the carboxy‐terminal half of the molecule. Sequence residues assumed to form clusters stabilizing the tertiary structure are highly conserved. Protein Z 4 is synthesized in the developing endosperm without a signal peptide and protein Z 4 mRNA was evenly distributed among the free and membrane‐bound polyribosomes of the endosperm cell. An internal hydrophobic region of 21 amino acids (residues 36–56) may serve as a signal for targeting the polypeptide into the lumen of the endoplasmic reticulum. The gene for protein Z 4 could not be detected in the barley variety Maskin and some of its descendants. The ‘high‐lysine’ allees, lysl (Hiproly barley) and lys3a (Bomi mutant 1508) on chromosome 7, enhance and repress, respectively, the expression of the protein Z 4 gene. Also, 1554 bp of another 8‐kbp fragment of the barley genome PazΨ , similar to the protein‐Z 4 ‐coding region, have been determined. Small insertions and deletions and the presence of an internal stop codon identify this fragment as part of a pseudogene related to the protein Z 4 gene.