Synthesis of ppGpp and chloroplast ribosomal RNA in Chlamydomonas reinhardi.

A material identified as guanosine 5',3'-bis-diphosphate (ppGpp) has been detected in extracts of Chlamydomonas reinhardi ac-20 cells grown under mixotrophic conditions or in arg-2 cells deprived of arginine. The material was acid and base labile, susceptible to alkaline phosphatase, resistant to periodate oxidation, had spectral characteristics of a guanine derivative and comigrated on chromatograms with ppGpp from Escherichia coli. In ac-20 ppGpp may be involved in the control of chloroplast ribosomal RNA synthesis. When ac-20 cells were shifted from mixotrophic to autotrophic conditions, the 32Pi labeling of ppGpp, relative to that of GTP, was reduced, while the specific labeling of chloroplast ribosomal RNA was enhanced. Addition of low concentrations of cycloheximide had somewhat similar effects.