Subunit stoichiometry of the Drosophila melanogaster small nuclear RNA activating protein complex (SNAPc).

Small nuclear RNA activating protein complex (SNAPc) is a multi-subunit transcription factor required for expression of small nuclear RNA genes. This protein binds to a promoter element located approximately 40-65 bp upstream of the transcription start site. In Drosophila melanogaster, DmSNAPc contains three distinct polypeptide subunits: DmSNAP190, DmSNAP50, and DmSNAP43. The subunit stoichiometry in SNAPc complexed with DNA has not been examined. Therefore, the ability of differently tagged but otherwise identical subunits to associate with each other into the same protein-DNA complex was assayed by antibody super-shift analysis. The results reveal that DmSNAPc contains only a single copy of each of the three subunits.