The SPR3 gene encodes a sporulation-specific homologue of the yeast CDC3/10/11/12 family of bud neck microfilaments and is regulated by ABFI.

The SPR3 gene is selectively activated only during the sporulation phase of the Saccharomyces cerevisiae (Sc) life cycle. The predicted amino acid (aa) sequence has homology to microfilament proteins that are involved in cytokinesis and other proteins of unknown function. These include the products of Sc cell division cycle (CDC) genes involved in bud formation (Cdc3p, Cdc10p, Cdc11p and Cdc12p), Candida albicans proteins that accumulate in the hyphal phase (CaCdc3p and CaCdc10p), mouse brain-specific (H5p) and lymphocyte (Diff6p) proteins, Drosophila melanogaster (Dm) protein Pnutp (which is localized to the cleavage furrow of dividing cells), a Diff6p homologue (DmDiff6p), and the Sc septin protein (Sep1hp), a homologue of the 10-nm filament proteins of Sc. One strongly conserved region contains a potential ATP-GTP-binding domain. Primer extension analysis revealed six major transcription start points (tsp) beginning at -142 relative to the ATG start codon. The sequence immediately upstream from the tsp contains consensus binding sites for the HAP2/3/4 and ABFI transcription factors, a T-rich sequence and two putative novel elements for mid to late sporulation, termed SPR3 and PAL. Electrophoretic mobility shift assay (EMSA) and footprint analyses demonstrated that the ABFI protein binds to a region containing the putative ABFI site in vitro, and site-directed mutagenesis showed that the ABFI motif is essential for expression of SPR3 at the appropriate stage in sporulating cells.