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

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Abstract
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 11 ts ) was allelic with PD2, another one (PD 12 ts ) was linked to PD3 and the third one (PD 13 ts ) was linked to PD2. PD 11 ts and PD 13 ts affected the formation of the neutral phosphatase only whereas PD 12 ts 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 Km values were found in WT, PD 11 ts and PD 12 ts 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 Km 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 12 ts and PD 13 ts mutations.