Multifaceted investigation of ribonuclease MRP in Cyanidioschyzon merolae: Heat stress response, canonical rRNA processing pathway, structural prediction and mutational analysis

RNase MRP is a ribonucleoprotein complex essential for ribosome biogenesis in eukaryotes including Saccharomyces cerevisiae and humans. Mutations in the single genomic locus encoding its noncoding RNA component result in cartilage-hair hypoplasia (CHH), a recessively inherited developmental disorder. In Cyanidioschyzon merolae, the 442-nucleotide RNA component of RNase MRP is encoded within the intronic region of the CMK142T gene. Under heat stress conditions, this intronic region accumulates significantly, prompting investigations into the effects of heat stress on RNase MRP expression and its role in 5.8S rRNA processing. The impact on 5.8S rRNA processing of deleting the P19 region (∆372–405) and the G162A mutation via homologous recombination was assessed using Northern blot analysis while computational analyses were performed to compare structural conservation and protein composition of RNase MRP in C. merolae with other eukaryotes. Total RNA analysis indicates that deletion of the P19 region (∆372–405) of MRP significantly alters the stoichiometry of 5.8S rRNA forms, underscoring its importance in rRNA processing. Additionally, C. merolae adheres to the canonical rRNA processing pathway and while rDNA transcription is inhibited under heat stress, the stability of mature 28S and 18S rRNA remains unaffected, indicating the organism's sophisticated regulatory mechanism in ribosome biogenesis. Computational comparative genomics analyses revealed conserved structural regions in C. merolae RNase MRP RNA, highlighting evolutionary conservation. The complex in C. merolae is predicted to comprise five proteins, fewer than the eleven in S. cerevisiae, reflecting dramatic streamlining of RNA processing pathways which parallels findings in pre-mRNA splicing. These findings confirm the conserved function of RNase MRP in C. merolae and raise important questions about why the levels appear to increase under heat stress.