TRA-1 is the terminal regulator of sex determination in C. elegans. TRA-1 is a zinc finger transcription factor, containing five zinc fingers, and is a member of the GLI family of transcription factors. The GLI family also includes cubitus interruptus (Ci) in Drosophila and the GLI proteins in mammals. Previously, we have identified a novel, post-transcriptional role for TRA-1. In the absence of TRA-1,
tra-2 mRNA is retained in the nucleus, indicating TRA-1 may be required for nuclear export of the
tra-2 mRNA. Our data suggests TRA-1 mediates this by binding the
tra-2 3'UTR. The TRA-1 binding site is separate from and 5' to the previously identified translational control elements in the
tra-2 3' UTR. Our working model is that in part TRA-1 promotes female development by binding the
tra-2 3'UTR to enhance export of the
tra-2 mRNA from the nucleus to the cytoplasm. Comparison of the known TRA-1 DNA binding site (Zarkower et. al., 1993) with the RNA binding site in the
tra-2 3'UTR indicates the sequences share no significant similarity. Our data suggests that RNA binding may be a conserved function among the GLI family members as GLI-1 also binds RNA. Using RNA gel shift analysis, we are investigating what domains of TRA-1 are responsible for RNA binding. Wild-type TRA-1 protein has three distinct regions, an amino-terminal domain, which contains a gain of function region, the 5 zinc fingers (1-5), in which only zinc fingers 3-5 bind DNA (Zarkower et. al., 1993), and a carboxy-terminal domain, which may contain a putative trans-activation domain. We find that protein containing the amino terminus and zinc fingers 1-5 also binds RNA, and protein containing the amino terminus and zinc fingers 1-2 binds RNA, although more weakly. However, protein consisting of only the amino terminus does not bind RNA. Preliminary results indicate the zinc fingers are critical for RNA binding since a protein consisting of only the five zinc fingers specifically binds the
tra-2 3'UTR. The fact that zinc fingers 1-2 bind RNA, but not DNA suggests the properties of how TRA-1 binds RNA will be distinct from that of DNA. We are presently testing whether zinc fingers 3-5 are involved in RNA binding.