The sex determining gene,
tra-2 proootes feDale development in XX animals (Hodgkin and Brenner). In adult hermaphrodites, transcripts of 5.0kb and 1.8kb are detected by Northern blot analysis (Okkema and Kimble). Expression of the 5.0kb transcript reveals no qualitative sex or temporal differences, however, the 1.8kb RNA shows sex, temporal and tissue specificity. The 5.0kb RNA is trans-spliced to
s1-2 and encodes a putative meDbrane associated protein of 1475 amino acids. The carboxy terminus is hydrophilic and we speculate that this region is important for
tra-2 regulation (see below). The 1.8kb RNA is colinear with the 3'end of the 5.0kb RNA based on RNase H mapping and PCR; this RNA is trans-spliced to sl-l at a site which is also used as a cis-splice acceptor by the 5.0kb RNA. The putative protein produced by tbe 1.8kb RNA, which has the same open reading frame as tbe 5.0kb RNA, consists of only the hydrophilic region. We propose that the tra- 2 protein is regulated by two distinct mechanisms. (l) In the hermaphrodite germline,
tra-2 is negatively regulated to allow spermatogenesis (Doniach);
fog-2 is a potential candidate to effect this regulation (Schedl and Kimble). The
tra-2 (mx) alleles (for Dixed character), show gain-offunction feminizing and loss-of-function rasculinizing effects. Each of tbe
tra-2 (ox) alleles is a missense mutation that generates a non-conservative amino acid change within 22 amino acids of the hydrophilic region. We postulate that the tra- 2 ( mx) alleles define a region for
fog-2 binding and also that
tra-2 activity is associated with the larger
tra-2 protein (encoded by tbe 5. 0kb RNA). In our model,
fog-2 inactivates the larger
tra-2 protein by binding to the mx region. This repression is relieved by the smaller
tra-2 protein (encoded by the 1.8kb RNA) which tikates
fog-2. (2) In XO males,
tra-2 activity is negatively regulated to allow male development; her-l is thought to be responsible for this negative regulation (Hodgkin). Holecular characterization (per. comm. Perry and Wood) and mosaic analysis (per. comm. Hunter and Wood) of her-l suggests that it encodes a small secreted protein that acts non- autonomously. We predict that
tra-2, which appears to be Dembrane associated, may function as a receptor that binds her-l and that binding of her-l to
tra-2 may interfere with
tra-2 activity; e.g. by preventing a conformational change sr dimerization essential for
tra-2 function.