Erythromycin resistance and the chloroplast ribosome in Chlamydomonas reinhardi.

Five classes of erythromycin-resistant mutants of Chlamydomonas reinhardi have been identified. Each class corresponds to a different genetic locus, three nuclear and two chloroplast. The three nuclear loci appear to be unlinked, while Conde et al. (1975) have shown that the two chloroplast loci are linked, but not allelic. Mutants in each class have a unique pattern of cross-resistance in vivo to other antibiotics (lincomycin, carbomycin, and cleocin) that affect chloroplast protein synthesis. The chloroplast ribosomes from each class have a distinctive erythromycin-binding reaction in vitro.--Haploid and diploid strains containing combinations of different genes affecting the chloroplast ribosome were constructed to probe ribosome structure. New phenotypes were obtained by such combinations, demonstrating interactions between the gene products of a number of loci specifying ribosome components.