TARGET GENE IDENTIFICATION - TARGET SPECIFIC TRANSCRIPTIONAL ACTIVATION BY 3 MURINE HOMEODOMAIN VP16 HYBRID PROTEINS IN SACCHAROMYCES-CEREVISIAE

The mammalian homeodomain proteins encoded by Hox genes play an import ant role in embryonic development by providing positional queues which define developmental identities along the anteroposterior axis of dev eloping organisms. These proteins bind DNA specifically through their homeodomain to sequences containing ATTA cores, and thereby are though t to exert their effect regulating downstream genes. Little is known a bout the specificity of binding of homeodomain proteins to their seque nces and the identity of their target genes. We have developed a trans criptional activation assay in yeast which employs a homeobox/VP16 fus ion gene as a transcriptional activator and a target construct in whic h test fragments of DNA are inserted upstream to a reporter gene. Usin g this assay, we compared transcriptional activation by three chimeric proteins containing the homeodomains of the mouse homeobox genes, Hox a-5, Hoxb-6, and Hoxc-8. When tested on previously defined target sequ ences, strong differential specificities of activation were observed. In an effort to identify enhancers that normally respond to homeodomai n transcriptional activators, random fragments of mouse genomic DNA we re cloned upstream of the reporter gene. Genomic DNA fragments with di stinct activation profiles were obtained and were found to share match es beyond the ATTA core with previously described enhancers. These res ults demonstrate that the transcriptional activation system in yeast c an be used as a convenient system to detect DNA motifs which bind home odomain proteins, and subsequently, to identify authentic target genes responsive to Hox gene proteins. (C) 1996 Wiley-Liss, Inc.