Structural compensation for the deficit of rRNA with proteins in the mammalian mitochondrial ribosome - Systematic analysis of protein components of the large ribosomal subunit from mammalian mitochondria

The mammalian mitochondrial ribosome (mitoribosome) is a highly protein-ric h particle in which almost half of the rRNA contained in the bacterial ribo some is replaced with proteins. It is known that mitochondrial translation factors can function on both mitochondrial and Escherichia coli ribosomes, indicating that protein components in the mitoribosome compensate the reduc ed rRNA chain to make a bacteria-type ribosome, To elucidate the molecular basis of this compensation, we analyzed bovine mitoribosomal large subunit proteins; 31 proteins were identified including 15 newly identified protein s with their cDNA sequences from human and mouse. The results showed that t he proteins with binding sites on rRNA shortened or lost in the mitoribosom e were enlarged when compared with the E. coli counterparts; this suggests the structural compensation of the rRNA deficit by the enlarged proteins in the mitoribosome.