CONSERVATION AND DIVERGENCE OF NF-Y TRANSCRIPTIONAL ACTIVATION FUNCTION

The CCAAT-binding protein NF-Y is involved in the regulation of a vari ety of eukaryotic genes and is formed in higher eukaryotes by three su bunits NF-YA/B/C. We have characterized NF-Y of the trematode parasite Schistosoma mansoni and studied the structure and the function of the SMNF-YA subunit. In this work, we present the cloning and sequence an alysis of the B subunit of the parasite factor. SMNF-YB contains the c onserved HAP-3 homology domain hut the remaining part of the protein w as found to be highly divergent from ail other species. We demonstrate d by transfections of GAL4 fusion constructs, that mouse NF-YB does no t contain activation domains while the C-terminal part of SMNF-YB has transcriptional activation potential. On the other hand, the N-termina l parts of SMNF-YA and mouse NF-YA were shown to mediate transactivati on; the integrity of a large 160 amino acid glutamine-rich domain of N F-YA was required for this function and an adjacent serine- and threon ine-rich domain was necessary for full activity in HepG2, but redundan t in other cell types. Transactivation domains identified in SMNF-YB a re also rich in serine and threonine residues. Our results indicate th at serine/threonine-rich sequences from helminth parasites potentiate transcription and that such structures have diverged during evolution within the same transcription factor.