Short tandem repeats shared by B- and C-hordein cDNAs suggest a common evolutionary origin for two groups of cereal storage protein genes.
We have identified cDNA clones coding for the major sulphur-rich and sulphur-poor groups of barley storage proteins (the B- and C-hordeins, respectively). Hybridization studies have revealed unexpected homologies between B- and C-hordein mRNAs. Using a deletion mutant (Risø 56), we have mapped some C-hordein-related sequences within, or closely associated with, B-hordein genes at the Hor 2 locus. Nucleotide sequencing has shown that the primary structure of B-hordein polypeptides can be divided into at least two domains: domain 1 (repetitive, proline-rich, sulphur-poor), which is homologous to C-hordein sequences, and domain 2 (non-repetitive, proline-poor, sulphur rich), which makes up two-thirds of the polypeptide and is partially homologous to a 2S globulin storage protein found in dicotyledons. The coding sequences that are homologous in B- and C-hordein mRNAs have an asymmetric base composition (>80% C-A) and are largely composed of a degenerate tandem repeat based on a 24 nucleotide consensus that encodes Pro-Gln-Gln-Pro-Phe-Pro-Gln-Gln. We discuss the evolutionary implications of the domain structure of the B-hordeins and the unusual relationship between the two groups of barley storage proteins.
Forde
B G
BG
Biochemistry Department, Rothamsted Experimental Station, Harpenden, Herts AL5 2JQ, UK.
Kreis
M
M
Williamson
M S
MS
Fry
R P
RP
Pywell
J
J
Shewry
P R
PR
Bunce
N
N
Miflin
B J
BJ
D000595:Amino Acid Sequence; D001483:Base Sequence; D005075:Biological Evolution; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D017353:Gene Deletion; D005983:Glutens; D001467:Hordeum / Q000235:genetics; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D020080:Tandem Repeat Sequences / Q000235:genetics*
D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; D005983:Glutens