Circadian synthesis of a nuclear-encoded chloroplast glyceraldehyde-3-phosphate dehydrogenase in the dinoflagellate Gonyaulax polyedra is translationally controlled.

ABSTRACT

The circadian clock has previously been shown to restrict synthesis of several proteins in the dinoflagellate Gonyaulax polyedra to only a few hours each day. We have identified one of these proteins as glyceraldehyde-3-phosphate dehydrogenase. Two nuclear genes encoding the enzyme have been cloned, one corresponding to a cytoplasmic isoform and the other to a plastid targeted protein. On the basis of protein microsequence data, we conclude that the synthesis of the plastid isoform is clock-regulated. This regulation is not related to mRNA levels, which remain constant throughout the cycle, suggesting a translational control mechanism, in contrast to the transcriptional regulation of GAPDH that has been demonstrated in Neurospora. Although the rhythm of synthesis has a high amplitude, the abundance and activity rhythms are greatly attenuated, which is attributed to the long half-life of the protein.