Protein deficient chloroplast ribosomes in a yellow mutant of Chlamydomonas reinhardii.

Ribosomes and ribosomal proteins from wild-type and a yellow mutant of Chlamydomonas reinhardii were analyzed and compared by two-dimensional gel electrophoresis. The mixothrophically grown yellow-76 mutant differs from wild-type cells in lowered chlorophyll content and photosynthetic activity per chlorophyll unit. The latter is connected with the decreased activity of the ribulose-I,5-diphosphate-carboxylase enzyme. Analytical ultracentrifugation of cell extracts shows a normal amount of free 70S ribosomes and 50S subunit in the mutant cells. Two-dimensional gel electrophoresis shows considerable alterations in the protein composition of the 70S ribosomes of the mutant. Two proteins are absent from the electrophoretograms of the yellow-76 mutant, and seven proteins are present in reduced amounts. The genetical analysis shows a Mendelian pattern of inheritance, indicating that protein alterations presumably are localized in nuclear DNA.