Stable insertion of the early light-induced proteins into etioplast membranes requires chlorophyll-alpha

Etiolated plant seedlings exposed to light respond by transient accumulatio n of the nucleus-encoded, plastid-located early light-inducible proteins (E lips), These proteins are distant relatives of the light-harvesting chlorop hyll a/b-binding gene family and bind pigments with unusual characteristics . To investigate whether accumulation of flips in plastid membranes is post -translationally regulated by pigments, reconstitution studies were perform ed, where in vitro transcribed and translated low molecular mass Elip precu rsors of barley were combined with lysed barley etioplasts complemented wit h various compositions of isolated pigments. We showed that the membrane in sertion of Elips, as proven by protease protection assays and washes with a chao-tropic salt or alkali, depended strictly on chlorophyll a but not on chlorophyll b or xanthophyll zeaxanthin. The amount of inserted Elips incre ased almost linearly with the chlorophyll a concentration, and the insertio n efficiency was not significantly influenced by a light intensity between 1 and 1,000 mu mol.m(-2).s(-1). In contrast, in vitro import of Elip precur sors into greening plastids was enhanced by high intensity light. Thus, we conclude that although chlorophylls bound to flips seem to not be involved in light harvesting, they are crucial for a stable insertion of these prote ins into the plastid membrane.