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

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 degrees C but not at 35 degrees C were isolated and investigated. One of these mutants (PDts11) was allelic with PD2, another one (PDts12) was linked to PD3 and the third one (PDts13) was linked to PD2. PDts11 and PDts13 affected the formation of the neutral phosphatase only whereas PDts12 interfered with the formation of both neutral and alkaline phosphatases at 35 degrees 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, PDts11 and PDts12 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 PDts12 and PDts13 mutations.