Interaction of seed nuclear proteins with transcriptionally-enhancing regions of the pea (Pisum sativum L.) legA gene promoter.

An 873-basepairs promoter fragment (-833 to +40), of the legA (legumin seed storage protein) gene of pea is known to be fully functional in transgenic plants. This fragment has been enzymically cleaved, and the products examined for the ability to interact specifically with nuclear proteins. Use of DNA-binding and mobility-shift assays has shown that promoter sequences between -316 and +40 do not form stable complexes with seed nuclear extracts. Fragments from -549 to -316 and -833 to -582, however, did interact strongly with seed, but not leaf, nuclear proteins. Each probe reacted similarly to form three distinct and stable complexes, although only the complex with least mobility appeared to be specific when challenged with competitor DNA fragments. Competitor studies also indicate that a single factor (designated LABF1) forms these specific low-mobility complexes with both probes. Fractionation of seed nuclear proteins by sodium dodecyl sulphate polyacrylamide gel electrophoresis, followed by elution and renaturation, shows that LABF1 activity resides in the 84 000- to 116 000-Mr size range of polypeptides. The tissue-specific activity of LABF1 is temporally correlated with legumin gene expression, a relationship consistent with suggestions that this factor may act as a transcriptional enhancer.