Cdna cloning of a novel heterogeneous nuclear ribonucleoprotein gene homologue in Caenorhabditis elegans using hamster prion protein cDNA as a hybridization probe

The mammalian prion protein (PrP^c) is a cellular protein of unknown function, an altered isoform of which (PrP^sc) is a component of the infectious particle (prion) thought to be responsible for spongiform encephalopathies In humans and animals. The evolutionary conservation of the PrP gene has been reported in the genomes of many vertebrates as well as certain invertebrates. In the genome of nematode Caenorhabditis elegans, the sequence capable of hybridizing with the mammalian PrP cDNA probe has been demonstrated, predicting the presence of the PrP gene homologue in C.elegans. In this study, Southern analysis with the hamster PrP cDNA (HaPrP) probe confirmed the previous observation. Moreover, Northern analysis revealed that the sequence is actively transcribed in adult worms. Thus, we screened C.elegans cDNA libraries with the HaPrP probe and isolated a cDNA that hybridizes to the same sequence in C.elegans that hybridized with the HaPrP probe in the Southern and Northern analyses. The deduced amino acid sequence of this cDNA, however, is substantially homologous with heterogeneous nuclear ribonucleoprotein (hnRNP) core proteins rather than mammalian PrP^c. The hnRNPs contain the glycine-rich domain in the C-terminal half of the molecule, which also seemed to be in PrP^° at the N-terminal half of the molecule. Both of the glycine-rich domains are composed of tracts with high G + C content, indicating that these tracts may due to the hybridizing signals. These results suggest that this cDNA clone is derived from a novel hnRNP gene homologue in C.elegans but not from a predicted PrP gene homologue.