Proteins of wheat bran. I. Isolation and elementary analyses of a globulin, albumin, and prolamine

A maize prolamin box (P-box)-binding factor (PBF-1) has been purified and characterized from immature endosperm tissue. PBF-1 has a molecular weight of 38 kDa. It is detected only in endosperm, but not in root or leaf tissues, consistent with its tissue-specific function. Site-directed mutagenesis experiments reveal that both the P-box and its flanking sequences are important for PBF-1 DNA binding. Developmental studies show that PBF-1 accumulates in the endosperm from 8 to at least 30 days after pollination (DAP). From 16 to 24 DAP, however, multiple shifted bands of protein(s)–DNA complexes can be observed, which correlate with an increase in zein gene expression. PBF-1 can also bind to the P-box from `22-kDa' and `19-kDa' zein promoters, but at a lower affinity than to the `27-kDa' zein promoter. The effects of protein dephosphorylation and zinc ion chelators on PBF-1 DNA binding activity are also shown. A model is proposed where PBF-1 serves as a `recruiter' of class-specific transcription factors like Opaque2 (O2).