Cloning and characterization of a cDNA encoding a rice 13 kDa prolamin

Area of Science:

• Plant Molecular Biology
• Biochemistry
• Genetics

Background:

• Rice endosperm stores proteins essential for seed development.
• Prolamins are a major class of seed storage proteins in cereals.
• Understanding prolamin structure and function is key to improving crop nutritional value.

Purpose of the Study:

• To isolate and characterize a 13 kDa prolamin from developing rice endosperm.
• To determine the amino acid sequence and identify conserved regions within the prolamin.
• To compare the rice prolamin with other cereal prolamins to understand evolutionary relationships.

Main Methods:

• Screening of a rice cDNA library with a high-frequency cDNA clone (lambda RM7).
• In vitro translation using a wheat germ cell-free system.
• Edman degradation for N-terminal amino acid sequencing.
• Nucleotide and amino acid sequence analysis for homology.

Main Results:

• A 13 kDa polypeptide was identified as the translation product of the screened mRNA.
• The deduced amino acid sequence revealed a polypeptide rich in hydrophobic residues and glutamine, lacking lysine.
• A conserved octapeptide sequence (Gln-Gln-Gln-Cys-Cys-Gln-Gln-Leu) was found, shared with other cereal prolamins.
• The signal sequence showed over 65% homology with rice 10 kDa prolamin and maize zein at both nucleotide and amino acid levels.

Conclusions:

• The 13 kDa rice prolamin exhibits characteristics consistent with its classification.
• Conserved sequences suggest functional or structural importance and evolutionary links among cereal prolamins.
• Homology in the signal sequence region indicates shared regulatory mechanisms or origins with related proteins.