Genes involved in the regulation of the neutral phosphatase in Chlamydomonas reinhardi

Summary

In Chlamydomonas reinhardi, mutations in either of two unlinked genes (PD₂ and PD₃) abolish the activity of the derepressible neutral phosphatase. The question arose whether these genes (or one of them) specify the structure of the enzyme or whether they have a regulatory function.

Three mutants producing an active phosphatase at 25°C but not at 35°C were isolated and investigated. One of these mutants (PD ^ts₁₁ ) was allelic with PD₂, another one (PD ^ts₁₂ ) was linked to PD₃ and the third one (PD ^ts₁₃ ) was linked to PD₂.

PD ^ts₁₁ and PD ^ts₁₃ affected the formation of the neutral phosphatase only whereas PD ^ts₁₂ interfered with the formation of both neutral and alkaline phosphatases at 35°C. The neutral phosphatase produced by the three mutants at low temperature was not more thermosensitive in vitro than the wild enzyme. Moreover, quite similar K_m values were found in WT, PD ^ts₁₁ and PD ^ts₁₂ using naphthyl phosphate as a substrate.

On the other hand, revertants of PD ^-₂ and PD ^-₃ were isolated: their neutral phosphatases could not be distinguished from the wild enzyme on the basis of their thermosensitivities and K_m values for naphthyl phosphate.

These results are consistent with the idea that PD₂ and PD₃ are regulatory genes. Other possible regulatory genes were revealed through PD ^ts₁₂ and PD ^ts₁₃ mutations.