A defective signal peptide in the maize high-lysine mutant floury 2.
The maize floury 2 (fl2) mutation enhances the lysine content of the grain, but the soft texture of the endosperm makes it unsuitable for commercial production. The mutant phenotype is linked with the appearance of a 24-kDa alpha-zein protein and increased synthesis of binding protein, both of which are associated with irregularly shaped protein bodies. We have cloned the gene encoding the 24-kDa protein and show that it is expressed as a 22-kDa alpha-zein with an uncleaved signal peptide. Comparison of the deduced N-terminal amino acid sequence of the 24-kDa alpha-zein protein with other alpha-zeins revealed an alanine to valine substitution at the C-terminal position of the signal peptide, a histidine insertion within the seventh alpha-helical repeat, and an alanine to threonine substitution with the same alpha-helical repeat of the protein. Structural defects associated with this alpha-zein explain many of the phenotypic effects of the fl2 mutation.
Coleman
C E
CE
Department of Plant Sciences, University of Arizona, Tucson 85721, USA.
Lopes
M A
MA
Gillikin
J W
JW
Boston
R S
RS
Larkins
B A
BA
D000595:Amino Acid Sequence; D001483:Base Sequence; D015139:Blotting, Southern; D003001:Cloning, Molecular; D015180:Electrophoresis, Gel, Two-Dimensional; D008040:Genetic Linkage; D008239:Lysine / Q000032:analysis*; D008969:Molecular Sequence Data; D009154:Mutation; D012150:Polymorphism, Restriction Fragment Length; D011498:Protein Precursors / Q000235:genetics; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000235:genetics*; D012639:Seeds / Q000737:chemistry / Q000235:genetics; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000737:chemistry / Q000235:genetics*; D015028:Zein / Q000737:chemistry / Q000235:genetics*
D011498:Protein Precursors; D021382:Protein Sorting Signals; D015028:Zein; D008239:Lysine