Chloramphenicol resistance mutations in the single 23S rRNA gene of the archaeon Halobacterium halobium

A broad range of antibiotics affecting protein biosynthesis were screened for their ability to inhibit growth of the archaeon Halobacterium halobium. Only a few drugs, including chloramphenicol, produced inhibitory effects. Mutants which showed increased resistance to chloramphenicol were isolated; of the nine tested, eight exhibited a C----U transition at position 2471 and the ninth had an A----C transversion at position 2088 of 23S rRNA. A double mutant containing both C----U (position 2471) and A----C (position 2088) mutations was isolated, but the level of its chloramphenicol resistance did not exceed that of either single-point mutant. Inferences are made concerning the functional significance of the conserved nucleotides in rRNAs.