ACCUMULATION OF A TRANSLATION INTERMEDIATE OF D1-PROTEIN BY LIGHT DARK TRANSITION IN ISOLATED SPINACH-CHLOROPLASTS

In an in vitro translation experiment using spinach chloroplasts, a novel protein band of about 17.5 kDa appeared by light to dark transition. The protein never accumulated in detectable amounts either in continuous illumination or in continuous darkness. The 17.5 kDa protein accumulated upon light-dark transition, on the other hand, disappeared by the subsequent illumination. Accumulation of the protein in light, however, was observed when stromal level of ATP in chloroplasts was lowered after preillumination by the addition of various chemical compounds which, irrespective of the mode of action, eventually decrease the ATP level, e.g. atrazine, carbonyl-cyanide-m-chlorophenyl hydrazone and glycerate. The dark-accumulated protein was concluded to be a translation intermediate of D1 protein based on the facts that this component precipitates with specific antibodies and is resistant to lysylendopeptidase treatment. The suppression by chloramphenicol of both appearance upon light dark transition and disappearance by the subsequent illumination of the protein also supported this conclusion. The phenomenon was discussed in terms of pausing in the translation of psbA mRNA.