Ribosomal protein SA and its pseudogenes in ruminants: an extremely conserved gene family

The ribosomal protein SA (RPSA), also known as 37-kDa laminin receptor precursor/67-kDa laminin receptor (LRP/LR), has been identified as a multifunctional protein, playing an important role in multiple pathologies like cancer and prion diseases. Since RPSA is involved in the binding and internalization of the prion protein, mutations in the ovine RPSA gene, influencing the RPSA-PrPC/PrPSc binding, can potentially play a part in the resistance to prion diseases. Our goal was to further characterize the complex RPSA gene family and to detect structural mutations which can play a role in this disease. In a prior study, 11 ovine pseudogenes were detected experimentally. As the whole genome shotgun ovine genome became accessible, an in silico genome-wide screening was performed and 37 new pseudogenes (36 processed and one semi-processed pseudogene) were detected, bringing the total to 48 ovine RPSA pseudogenes. Additionally, the complete bovine genome was screened in silico and 56 pseudogenes were identified. Once these sequences were known, it was possible to analyze the presence of mutations in the coding sequence and exon-flanking regions of the ovine functional full-length RPSA gene without the interference of pseudogenic sequences. Nineteen mutations were found: one in the 5' UTR, a silent one in the coding region, and seventeen in the exon-flanking regions, including an interesting mutation in the SNORA62 gene, localized in intron 4 of RPSA, leading to potential ribosomal defects. Structural mutations of the RPSA gene can be ruled out to play a role in transmissible spongiform encephalopathies but regulatory mutations still can have an effect on these diseases.