The essential gene for RNase MRP RNA, mrp1, was identified previously in Schizosaccharomyces pombe by homology to mammalian RNase MRP RNAs. Here we describe distinct site‐specific mutations in RNase MRP RNA that support a conserved role for this ribonucleoprotein in nucleolar 5.8S rRNA processing. One characterized mutation, mrp1‐ND90, displays dominance and results in accumulation of unspliced precursor RNAs of dimeric tRNA(Ser)‐tRNA(Met)i, suggesting a novel nuclear role for RNase MRP in tRNA processing. Cells carrying the mrp1‐ND90 mutation, in the absence of a wild‐type copy of mrp1, additionally require the mitochondrially associated nuclear mutation ptp1–1 for viability. Analysis of this mrp1 mutation reinforces previous biochemical evidence suggesting a role for RNase MRP in mitochondrial DNA replication. Several mutations in mrp1 result in unusual cellular morphology, including alterated nuclear organization, and are consistent with a broader nuclear role for RNase MRP in regulating a nuclear signal for septation; these results are a further indication of the multifunctional nature of this ribonucleoprotein.