Gene structure, protein structure, and regulation of the synthesis of a sulfur-rich protein in pea seeds

Identification and isolation of methionine-cysteine rich proteins in soybean seed

We recently developed a method to identify methionine-containing proteins and quantitate their methionine contents. We applied this method to soybeans and identified relatively methionine-rich proteins (MRP) among the albumins. By acidic methanol extraction of the albumins, we obtained a group of low molecular weight methionine-cysteine rich proteins (MCRP) that analyzed 4.0% methionine and 8.8% cysteine. MCRP made up 1-2% of the total protein in soybeans. Reversed-phase HPLC purification of MCRP yielded a protein peak that exhibited a single major band on denaturing polyacrylamide gel electrophoresis, had a molecular weight of 16 kD and contained 6.2% methionine and 18.8% cysteine. We are cloning the gene for this protein. Increasing its level through genetic engineering could increase the methionine-cysteine content of soybeans.

Sequence and expression of a gene encoding an albumin storage protein in sunflower

The complete sequence of a sunflower (Helianthus annuus) gene, HaG5, encoding a 2 S albumin storage protein was determined. The predicted unprocessed precursor has 295 amino acids, is rich in glutamine residues (24%) and contains a hydrophobic amino-terminus that is similar to the consensus signal peptide. Amino acid sequencing of the mature protein revealed extensive post-translational processing. Nuclease protection and primer extension analysis indicated a major transcriptional start 30 nucleotides 5' of the predicted ATG start codon. Additional sequence data, determined from a nearly full length cDNA recombinant, indicate that HaG5 is a member of a small gene family comprised of at least two divergent genes. Comparison of the predicted HaG5 gene product with sequences of other known plant proteins revealed distant but significant homology with the napins of Brassica and other heterogeneous seed proteins in the albumin superfamily.

cDNA and protein sequence of a major pea seed albumin (PA 2 : Mr≈26 000)

Pea albumin 2 (PA2:Mr≈26000) is a major component of the albumin fraction derived from aqueous salt extracts of pea seed. Sodium dodecylsulfate-polyacrylamide gel electrophoresis and chromatography on DEAE-Sephacel resolve PA2 into two closely related components (PA2a and PA2b). A cDNA clone coding for one of these components has been sequenced and the deduced amino acid sequence compared with partial, chemically-determined sequences for cyanogen bromide peptides from both PA2 components. Complete amino acid sequences were obtained for the C-terminal peptides. The PA2 molecule of 230 amino acids contains four imperfect repeat sequences each of approximately 57 amino acids in length.The combined sequence data, together with a comparison of PA2-related polypeptides produced in vitro and in vivo, indicate that PA2 is synthesized without a signal sequence and does not undergo significant post-translational modification. Although both forms of PA2 contain Asn-X-Thr consensus sequences, neither form is glycosylated. Accumulation of PA2 contributes approximately 11% of the sulfur-amino acids in pea seeds (cysteine plus methionine equals 2.6 residues percent). Suppression of levels of PA2 polypeptides and their mRNAs in developing seeds of sulfur-deficient plants is less marked than that for legumin, in spite of the lower content of sulfur-amino acids in legumin.