ATP-DEPENDENT PROTEIN-SYNTHESIS IN ISOLATED PEA-CHLOROPLASTS - EVIDENCE FOR ACCUMULATION OF A TRANSLATION INTERMEDIATE OF THE D1 PROTEIN

In the presence of externally added ATP, in the dark, isolated pea chloroplasts accumulate two proteins of molecular masses of about 22 and 24 kDa which precipitate with specific antibodies raised against the D1 protein. By chasing in the light, these proteins disappeared on the fluorogram concomitant with the appearance of the precursor- and mature-sized D1 proteins. Polysome analysis indicated that the 22-kDa component is associated with membrane-bound ribosomes and is thus ascribed to a translation intermediate of the D1 protein. On the other hand, the 24-kDa component could not be found in the polysome fraction under the experimental condition used, suggesting the possibility that this component is a degradation product of the D1 protein. The conclusion from this analysis is that the synthesis and/or stable accumulation of the D1 protein requires factor(s) caused by illumination, in addition to ATP, in isolated pea chloroplasts.