Beschreibung:
<jats:p>Ribosomes from three mutant strains of <jats:italic>Chlamydomonas reinhardi</jats:italic> were analysed in the analytical ultracentrifuge. The mutants were streptomycin sensitive and streptomycin resistant with a medelian and a uniparental pattern of inheritance of streptomycin resistance. At low ionic strength, the dissociation of the 70‐S ribosomes from the sensitive and the mendelianresistant strain is greater and their dimerisation smaller than in the uniparental mutant. On the other side the ultracentrifugation pattern of the ribosomal fraction of the sensitive strain is different from that of the two resistant strains. In experiments <jats:italic>in vivo</jats:italic>, streptomycin prevents the dissociation of the 70‐S ribosomes and induces the formation of 100‐S dimers. These “stick‐ ing effects” are greatest in the sensitive strain and smallest in the uniparental resistant mutant. It is suggested that in the two resistant mutants two different proteins of the 70‐S ribosomes are altered and that the streptomycin resistance of the uniparental mutant is localized in the chloroplast ribosomes. This assumption is strengthend by the finding that in the uniparental mutant the chloroplast ribosomes are streptomycin resistant, as measured by the ribulose 1,5‐bisphos‐ phate activity, whereas in the chromosomal‐resistant mutant they are streptomycin sensitive.</jats:p>