O. Lotan et al., HIGH-LEVELS OF PHOTOSYSTEM-I SUBUNIT-II (PSAD) MESSENGER-RNA RESULT IN THE ACCUMULATION OF THE PSAD POLYPEPTIDE ONLY IN THE PRESENCE OF LIGHT, The Journal of biological chemistry, 268(22), 1993, pp. 16185-16189
The light-regulated mRNA and polypeptide accumulation of the nuclear e
ncoded subunit II (PsaD) of the photosystem I reaction center was stud
ied during the greening of etiolated spinach seedlings. Upon exposure
to continuous white light, the mRNA, detected at low levels in etiolat
ed seedlings, accumulated in a specific pattern. In contrast, the PsaD
subunit could not be detected in the etiolated seedlings; the polypep
tide could first be detected in thylakoid membranes approximately 4 h
after exposure to continuous light. A pulse of red light induced the e
xpression of the PsaD mRNA, but the polypeptide could not be detected
unless the seedlings were exposed to light. In the light (but not in t
he dark), the PsaD mRNA was found associated with the polysomal fracti
on. Taken together, the data suggest a dual regulatory mechanism in wh
ich both the level of mRNA and the presence of light control the accum
ulation of the PsaD polypeptide.