The b-32 protein from endosperm: nucleic acid (c-DNA) and amino acid sequences

The b-32 protein is a maize endosperm albumin that apparently is not bound to any particulate cytoplasmic structure. Its expression during development is temporarily and quantitatively coordinated with that of zein storage proteins. The b-32 protein is found either in the acidic or in the basic form in all inbreds as a gene product of two codominant alleles. It has been shown that the o2 and o6 mutants lack this protein. This makes the protein a candidate to be a trans-acting factor involved in the positive regulation of storage protein genes. A full length c-DNA for the b-32 mRNA has been cloned and the complete amino acid sequence of the protein derived. A lambda gt11 library from immature endosperm was screened for the expression of the b-32 protein using antibodies against the purified protein. The nucleotide sequence shows that several internal gene duplications have taken place during evolution. The protein has a length of 303 residues (MW of 31979 daltons) and its sequence shows several outstanding features: no signal peptide is detectable, indicating that b-32 protein probably is not a secretory protein; it contains 6 Trp, a residue that is absent in maize storage proteins; polar and hydrophobic residues spread out along the whole sequence; several pairs of basic residues are detectable at the N-terminal region (res 1-70); the half C-terminal region of the molecule is rich in repeats either of the same residue or of groups of two or three residues; secondary structure predictions suggest two structural domains that would fold up giving rise to a globular protein

N. Di Fonzo, H. Hartings, M. Brembilla, M. Motto, C. Soave, F Salamini, E. Navarro and J. Palau


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