THE BIFACTORIAL ENDOSPERM BOX OF GAMMA-ZEIN GENE - CHARACTERIZATION AND FUNCTION OF THE PB3 AND GZM CIS-ACTING ELEMENTS

The proximal region of the gamma-zein promoter (gamma Z) has a functio nal bifactorial prolamin box element containing two cis-acting element s, a prolamin-box motif (Pb3) and a GCN4-like motif (GZM). By particle bombardment of maize endosperms with 5' deletions and internal deleti ons of gamma Z fused to the GUS gene, we have shown that a 135 bp regi on containing the bifactorial element is involved in the transcription al activation of the gamma Z promoter. However, the 135 bp region was unable to activate the gamma Z promoter in the absence of a 84 bp down stream sequence. Using in vivo footprinting and gel mobility shift ass ays with 15 DAP endosperm nuclear extracts, we have demonstrated the p resence of trans-acting factors that interact with Pb3 and GZM target sites. Base-substitution mutations within Pb3 and GZM decreased transc ription activity of the gamma Z promoter suggesting a co-ordinated fun ction between the two cis-acting elements. Two additional cis-motifs u pstream of the bifactorial prolamin element have been identified: a mo tif with high homology to the AACA elements of rice glutelin genes and an AZM motif containing an ACGT core which binds nuclear proteins oth er than the Opaque 2 (O2).