A single nucleotide substitution at the rib2 locus of the yeast mitochondrial gene for 21S rRNA confers resistance to erythromycin and cold-sensitive ribosome assembly

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Abstract
We have studied a mutation (cs23) in the mitochondrial gene for 21SrRNA that affects the peptidyl transferase center of the ribosome and conditionally blocks the assembly of the 54S ribosomal subunit. Strains carrying this mutation are resistant to erythromycin and cold-sensitive for growth on nonfermentable carbon sources (Singh et al. 1978) Mitochondria isolated from mutant cells grown on glucose at 20°C, the nonpermissive temperature, were depleted of the 54S subunit and instead contained a novel 45S ribosomal particle. After mutant cells were shifted from 20°C to 32°C, 54S subunits were assembled, apparently from the 45S particles and pre-existing ribosomal proteins. DNA sequencing revealed that the mutant phenotype is a consequence of a C to A transversion at position 3993 of the 21SrRNA gene. Previously, C to U and C to G mutations have been identified at the same position in the 21S rRNA sequence. This position corresponds to C-2611 in the E. coli 23S RNA, a nucleotide that appears to be conserved in the large rRNA of all erythromycin-sensitive ribosomes.