The activation domain of the maize transcription factor Opaque-2 resides in a single acidic region

Abstract

The maize (Zea mays L.) endosperm;specific transcription factor, encoded by the Opaque-2(02) locus, functions in vivo to activate transcription from its target promoters. 02 regulates the expression of a major storage protein class, the 22 kDa zeins, and of a type 1 ribosome inactivating protein, b-32, during maturation phase endosperm development. The coding sequence of 02, which indicates it to be a member of the basic region-leucine zipper (bZIP) class of DNA-binding proteins, contains a number of regions rich in either proline or acidic residues which are candidates for activation domains. In functional assays using tobacco mesophyll protoplasts, the level of transactivation conferred by a series of 02-deletion constructs was tested using as a reporter a fusion of the b-32 target promoter to β-glucuronidase (GUS). The results indicate that 02 has a single acidic activation domain, located near the M-terminus of the protein (amino acids 41-91). The ability of a Shorter part of this domain (amino acids 39-82) to confer transactivation was also demonstrated in domain swapping experiments, using fusions of the 02 polypeptide sequence to the: DNA-binding domain of the parsley (Petroselinum crispum) transcription factor CPRF1.