Subategory:

Mutants

Description:

The 68-4PP chloroplast mutant was isolated by screening for temperature-conditional, acetate-requiring mutants. It can grow on minimal medium at 25 °C, but dies on minimal medium at 35 °C. It results from an rbcL missense mutation that changes the codon for Leu-290 (CTT) to Phe (TTT), which causes a decrease in Rubisco CO₂/O₂ specificity and holoenzyme stability. The x-ray crystal structure has been solved. Selection for photosynthesis-competent revertants at the restrictive temperature has identified intragenic (R96-4C, R96-8E) and rbcS-intergenic (R88-5A, R116-1B, R116-10C) suppressors. This strain was recovered from a cross between the original 68-4PP mt+ and pf2 mt-, and has been maintained with acetate medium in darkness to prevent selection for secondary mutations that may improve Rubisco function or stability.

Species:

Chlamydomonas

Locus:

rbcL

Chromosome:

Chloroplast

Phenotype:

Requires acetate at 35 °C; temperature-conditional