Molecular phenotype of a human lymphoblastoid cell-line homoplasmic for the np 7445 deafness-associated mitochondrial mutation

Hum Mol Genet. 1997 Mar;6(3):443-9. doi: 10.1093/hmg/6.3.443.


We have studied mitochondrial gene expression and metabolic function in a human lymphoblastoid cell-line homoplasmic for the np 7445, deafness-associated mitochondrial DNA mutation. The mutation maps to the 3' termini of the oppositely oriented genes encoding cytochrome oxidase subunit I (COI) and tRNA-ser(UCN). In comparison with control lymphoblastoid cells, we detected a marked depletion (> 60%) of tRNA-ser(UCN). There was, however, no significant impairment of respiratory function, no alteration to the structure or abundance of COI mRNA or its precursors, and no detectable abnormality of mitochondrial protein synthesis. We also found considerable tissue-variation in the abundance of tRNA-ser(UCN). We propose that the tissue-specific phenotype associated with this mutation results from an inherent deficiency in the processing of the mutant pre-tRNA, that becomes limiting for protein synthesis only in a restricted set of cells of the auditory system in which the tRNA is, for other reasons, already at a critically low level.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blotting, Northern
  • Cell Line, Transformed
  • Cell Respiration
  • Culture Media
  • DNA, Mitochondrial / genetics*
  • Deafness / genetics*
  • Deafness / metabolism
  • Deoxyribonucleases, Type II Site-Specific / metabolism
  • Electron Transport Complex IV / chemistry
  • Electron Transport Complex IV / genetics
  • Galactose / metabolism
  • Genotype
  • Humans
  • Mitochondria / genetics
  • Mitochondria / metabolism*
  • Mutation*
  • Polymerase Chain Reaction
  • Protein Biosynthesis
  • Protein Synthesis Inhibitors / pharmacology
  • RNA Precursors / genetics
  • RNA, Transfer, Ser / genetics
  • RNA, Transfer, Ser / metabolism


  • Culture Media
  • DNA, Mitochondrial
  • Protein Synthesis Inhibitors
  • RNA Precursors
  • RNA, Transfer, Ser
  • Electron Transport Complex IV
  • endodeoxyribonuclease XBAI
  • Deoxyribonucleases, Type II Site-Specific
  • Galactose