Vol. 14, No. 24, pp. 3153-3165, December 15, 2000

RESEARCH PAPER
Direct protein-protein interaction between the intracellular domain of TRA-2 and the transcription factor TRA-1A modulates feminizing activity in C. elegans

¹ Department of Molecular and Medical Genetics, University of Toronto, Toronto, M5S 1A8, Canada; ² The Sanger Centre, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK; ³ Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota 55455, USA

In the nematode Caenorhabditis elegans, the zinc finger transcriptional regulator TRA-1A directs XX somatic cells to adopt female fates. The membrane protein TRA-2A indirectly activates TRA-1A by binding and inhibiting a masculinizing protein, FEM-3. Here we report that a part of the intracellular domain of TRA-2A, distinct from the FEM-3 binding region, directly binds TRA-1A. Overproduction of this TRA-1A-binding region has tra-1-dependent feminizing activity in somatic tissues, indicating that the interaction enhances TRA-1A activity. Consistent with this hypothesis, we show that tra-2(mx) mutations, which weakly masculinize somatic tissues, disrupt the TRA-2/TRA-1A interaction. Paradoxically, tra-2(mx) mutations feminize the XX germ line, as do tra-1 mutations mapping to the TRA-2 binding domain. We propose that these mutations render tra-2 insensitive to a negative regulator in the XX germ line, and we speculate that this regulator targets the TRA-2/TRA-1 complex. The intracellular domain of TRA-2A is likely to be produced as a soluble protein in vivo through proteolytic cleavage of TRA-2A or through translation of an XX germ line-specific mRNA. We further show that tagged derivatives of the intracellular domain of TRA-2 localize to the nucleus, supporting the hypothesis that this domain is capable of modulating TRA-1A activity in a manner reminiscent of Notch and Su(H).

[Key Words: Sex determination; signal transduction; development; receptor; Gli; two-hybrid]