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 b ody patterning morphogen, the Bicoid protein, requires both localization an d translational regulation of the maternal bicoid mRNA. Here we provide evi dence that the bicoid mRNA is also selectively stabilized during oogenesis, We identify and isolate a protein, BSF, that binds specifically to IV/V RN A, a minimal form of the bicoid mRNA 3 ' untranslated region that supports a normal program of mRNA localization during oogenesis, Mutations that disr upt the BSF binding site in IV/V RNA or substantially reduce the level of B SF 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 charact erized RNA binding motifs, However, BSF does include multiple copies of the PPR motif, whose function is unknown but appears in other proteins :vith r oles in RNA metabolism.