Functional mapping of the GAGA factor assigns its transcriptional activityto the C-terminal glutamine-rich domain

GAGA is a nuclear protein encoded by the Trithorax-like gene in Drosophila that is expressed in at least two isoforms generated by alternative splicin g. By means of its specific interaction with DNA, GAGA has been involved in several nuclear transactions including regulation of gene expression. Here we have studied the GAGA(519) isoform as a transcription factor. In vitro, the transactivation domain has been assigned to the 93 C-terminal residues that correspond to a glutamine-rich domain (Q-domain). It presents an inte rnal modular structure and acts independently of the rest of the protein. I n vivo, in Drosophila SL2 cells, Q-domain can transactivate reporter genes either in the form of GAGA or Gal4BD-Q fusions, whereas a GAGA mutant delet ed of the Q-domain cannot. Our results give support to the notion that GAGA can function as a transcription activating factor.