The sera of patients suffering from autoimmune diseases such as systemic lupus erythematosus and Silgren's syndrome often contain autoantibodies that target components of the Ro ribonucleoproteins (RoRNP). In human, these RoRNP are madeup of at least one major protein of 60 kDa, Ro60, and one of four small RNAs, hY RNAs. The La protein, which is a RNA polymerase III transcription termination factor, is also transiently associated with the complex by binding the poly(U) tail of the hY RNA. Although Ro60 has been implicated in the quality control of 5S rRNA production, the cellular role(s) of RoRNP remains elusive. In order to establish a genetic system for the the study of RoRNP genes, we have isolated the gene
rop-1, encoding the C. elegans homologue of Ro60. A single copy of this gene is located on the right arm of chromosome V, near genetic marker
unc-42 (cosmid C47A8), and it contains a 643 codon long open reading frame which is interupted by three introns. The encoded protein, Rop1p, shares 40% identity and 60% similarity with both human and Xenopus Ro60. Expression studies in transgenic N2, using a construct that places lacZ under the control of
rop-1 promoter, indicate that
rop-1 is expressed in every somatic cell of the organism. Disruption of
rop-1 by insertion of transposon Tc1 results in the production of truncated mRNA, leading to a complete knock-out of the expression of Rop1p. Moreover, we observe an increase in the level of the aberrant mRNA compared to wild type, which could suggest an autoregulation of the
rop-1 promoter by Rop1p itself. Nevertheless, no visible phenotype is associated with this deletion. This result is quite surprising considering the level of conservation of Rop1p throughout species. We have recently sequenced a cDNA,
yk74a1, encoding the C. elegans homologue of the La protein (CeLa). This protein contains 445 amino acids (50 kDa) and is fairly similar to its homologues in other species. The gene encoding CeLa is located on chromosome I, near genetic marker
unc-57 (cosmid C44E4). Interestingly, immunoprecipitation of Rop1p using specific anti-Rop1p antibodies show a stable association between Rop1p and a second protein of 50 kDa whose identity has not yet been confirmed.