A novel shuttle protein binds to RNA helicase A and activates the retroviral constitutive transport element

The constitutive transport element (CTE) of type D retroviruses mediates th e nuclear export of unspliced viral transcripts. We previously showed that RNA helicase A functionally interacts with CTE and contains a bidirectional nuclear transport domain at the carboxyl terminus. Here we report the iden tification of a novel human protein, helicase A-binding protein 95 (HAP95), which specifically binds to the carboxyl terminus of RNA helicase A HAP95 is partially homologous to AKAP95, a member of the A kinase-anchoring prote in family, but lacks the protein kinase A binding domain characteristic of this family. HAP95 is a nuclear protein at steady state but shuttles betwee n the nucleus and cytoplasm. Overexpression of HAP95 significantly increase s CTE-dependent gene expression but has no effect on general gene expressio n or that mediated by the Rev/Rev response element of human immunodeficienc y virus type 1.