During maturation of spermatids to motile spermatozoa in Caenorhabditis elegans, large vesicles called membranous organelles (MOs) fuse with the spermatid plasma membrane. Mutations in the gene fer-1 cause abnormal spermatozoa in which the MOs do not fuse, although they abut the plasma membrane normally. Here we describe the fer-1 gene, which we found to be approximately 8.6 kb in length and to encode a 6.2 kb transcript whose expression is limited to the primary spermatocytes, the cells in which the MOs form. fer-1 is predicted to encode a 235 kDa protein which is highly charged except for a putative transmembrane domain near the C terminus. We identified the mutations associated with five fer-1 alleles, all of which are missense mutations causing single amino acid changes. FER-1 is not similar to any characterized proteins in sequence databases, nor does it contain known functional motifs other than the predicted transmembrane domain. The C-terminal transmembrane domain makes FER-1 resemble some viral fusion proteins, suggesting it may play a direct role in MO-plasma membrane fusion. FER-1 does show significant sequence similarity to several predicted human proteins of unknown function. Two of the identified fer-1 mutations are located in regions of similarity between FER-1 and two of these predicted proteins. This strengthens the biological significance of these similarities and suggests these regions of similarity represent functionally important domains of FER-1 and the human proteins.
- © 1997 by Company of Biologists