Functional analysis of the Schistosoma mansoni 28 kDa glutathione S-transferase gene promoter: involvement of SMNF-Y transcription factor in multimeric complexes.

The ability of the 5' flanking region of the gene encoding the 28 kDa glutathione S-transferase of Schistosoma mansoni gene to promote transcription, was studied in different mammalian cell lines. Results of transient transfection assays showed a strong activity of the -277 to +1 nt region of the Sm28GST gene, comparable to that of well-studied promoters. Deletion analysis indicated that an AP-1 site and two closely located CCAAT (Y1 and Y2) boxes were the principal motifs responsible for the promoter activity. Binding of the NF-Y complex to Y1 and Y2, as well as to a third CCAAT box (Y3) close to the promoter TATA box, was compared in gel shift and super-shift experiments. All of the three Y boxes bound protein complexes from S. mansoni nuclear extracts that were shown to contain the A subunit of the schistosome NF-Y complex (SMNF-YA). Competition assays revealed a differential affinity of the Y1, Y2 and Y3 sequences for NF-Y. The Y1, Y2 and Y3 regions were also shown to activate transcription when included in an heterologous promoter and data obtained strongly suggested the involvement of SMNF-Y in multimeric complexes during this process.