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Nuclear mutations affect the catalysis, stability, and expression of chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase in Chlamydomonas reinhardti
Abstract
Nuclear mutants 68-11AR, 70-5Y, and 72-7JJ have temperature-conditional phenotypes because they fail to accumulate a normal level of Rubisco at $35\sp\circ\rm C.$ These nuclear mutations are not allelic to each other, and they are not linked to the Rubisco small-subunit genes. Mutant 68-11AR is similar to 68-4PP in that it has a temperature-conditional phenotype, and its Rubisco has a reduced $\rm CO\sb2/O\sb2$ specificity. However, the S52-2B mutation does not suppress the temperature-conditional phenotype of 68-11AR, indicating that the 68-11AR and 68-4PP Rubisco enzymes are altered in different ways. Rubisco enzymes purified from 70-5Y and 72-7JJ also have altered kinetic constants. It thus appears that the 68-11AR, 70-5Y, and 72-7JJ nuclear mutations influence Rubisco at posttranslational steps. Mutant 76-5EN has a nonconditional, acetate-requiring phenotype due to a nuclear-gene mutation that blocks rbcL transcription. The 76-5EN gene product interacts with the basic rbcL promoter. Revertant selection identified several nuclear suppressor mutations. One suppressor, named S107-4B, is unique because it confers a temperature-conditional phenotype when separated from the original 76-5EN mutation. Even though the S107-4B mutation increased rbcL expression in 76-5EN at $25\sp\circ\rm C,$ it blocked the accumulation of atpA mRNA at $35\sp\circ\rm C.$ Genetic analysis revealed that the S107-4B gene is not an allele of the 76-5EN gene. It thus appears that at least two different nuclear gene products are involved in the differential transcription of chloroplast genes in C. reinhardtii.
Subject Area
Biochemistry|Molecular biology|Botany
Recommended Citation
Hong, Seokjoo, "Nuclear mutations affect the catalysis, stability, and expression of chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase in Chlamydomonas reinhardti" (1996). ETD collection for University of Nebraska-Lincoln. AAI9715966.
https://digitalcommons.unl.edu/dissertations/AAI9715966