SEQUENCE-ANALYSIS OF MITOCHONDRIAL CHLORAMPHENICOL RESISTANCE MUTATIONS IN CHINESE-HAMSTER CELLS

A series of mitochondrially inherited chloramphenicol-resistant (CAP-R ) mutants were isolated in Chinese hamster cells. To determine whether the Chinese hamster CAP-R mutations were homologous to those isolated in mouse and human cell culture systems, we determined the nucleotide sequence of the region of the mitochondrial 16S rRNA gene spanning th e peptidyl transferase-encoding region for eight CAP-R mutant lines in addition to the parental wild-type line. Three main conclusions are d rawn from these studies. (1) Although the region of the gene encoding the peptidyl transferase domain is highly conserved relative to that o f mice and rats, the contiguous sequences show less conservation. This sequence divergence not only includes the accumulation of single base pair replacements, but also the presence of small insertions or delet ions. (2) For six of the CAP-R mutants, heteroplasmic single base pair changes were detected. These mapped to the same sites within the pept idyl transferase domain as the mutations found previously in mouse and human CAP-R mutants. (3) Two Chinese hamster CAP-R mutants, both with an unusual drug resistance phenotype, did not carry any mutations wit hin the CAP-R peptidyl transferase domain. However, both carried a het eroplasmic mutation at the position corresponding to nucleotide 2505 o f the mouse 16S rRNA gene, a site predicted to map within a stem/loop structure attached to this key domain of the ribosome. This is the fir st evidence for mitochondrial CAP-R mutations that map outside the pep tidyl transferase region.