BSF binds specifically to the bicoid mRNA 3' untranslated region and contributes to stabilization of bicoid mRNA

The early stages of Drosophila melanogaster development rely extensively on posttranscriptional forms of gene regulation. Deployment of the anterior body patterning morphogen, the Bicoid protein, requires both localization and translational regulation of the maternal bicoid mRNA. Here we provide evidence that the bicoid mRNA is also selectively stabilized during oogenesis. We identify and isolate a protein, BSF, that binds specifically to IV/V RNA, a minimal form of the bicoid mRNA 3' untranslated region that supports a normal program of mRNA localization during oogenesis. Mutations that disrupt the BSF binding site in IV/V RNA or substantially reduce the level of BSF protein lead to reduction in IV/V RNA levels, indicating a role for BSF in RNA stabilization. The BSF protein is novel and lacks all of the characterized RNA binding motifs. However, BSF does include multiple copies of the PPR motif, whose function is unknown but appears in other proteins with roles in RNA metabolism.