02618nas a2200493   4500000000100000000000100001008004100002260001500043653002400058653001600082653002500098653001900123653002500142653003300167653003800200653001700238653002800255653001000283653002800293653002200321653003000343653002000373653002200393653001900415653002400434653003800458653001500496653002600511653003300537100002100570700002200591700002300613700001900636700002100655700002400676700001900700700003100719700002200750245010700772300001100879490000800890520121200898022001402110       2008                            d  c2008 Jul 110aAmino Acid Sequence10aArabidopsis10aArabidopsis Proteins10aBacteriophages10aDNA-Binding Proteins10aDNA-Directed RNA Polymerases10aGene Expression Regulation, Plant10aGene Library10aIntracellular Membranes10aLight10aMolecular Sequence Data10aOrgan Specificity10aPromoter Regions, Genetic10aProtein Binding10aProtein Transport10aRNA, Messenger10aRNA, Ribosomal, 16S10aSaccharomyces cerevisiae Proteins10aThylakoids10aTranscription Factors10aTwo-Hybrid System Techniques1 aJacinthe Azevedo1 aFlorence Courtois1 aMohamed-Ali Hakimi1 aEmilie Demarsy1 aThierry Lagrange1 aJean-Pierre Alcaraz1 aPankaj Jaiswal1 aLaurence Maréchal-Drouard1 aSilva Lerbs-Mache00aIntraplastidial trafficking of a phage-type RNA polymerase is mediated by a thylakoid RING-H2 protein.  a9123-80 v1053 aThe plastid genome of dicotyledonous plants is transcribed by three different RNA polymerases; an eubacterial-type enzyme, PEP; and two phage-type enzymes, RPOTp and RPOTmp. RPOTp plays an important role in chloroplast transcription, biogenesis, and mesophyll cell proliferation. RPOTmp fulfills a specific function in the transcription of the rrn operon in proplasts/amyloplasts during seed imbibition/germination and a more general function in chloroplasts during later developmental stages. In chloroplasts, RPOTmp is tightly associated with thylakoid membranes indicating that functional switching of RPOTmp is connected to thylakoid association. By using the yeast two-hybrid system, we have identified two proteins that interact with RPOTmp. The two proteins are very similar, both characterized by three N-terminal transmembrane domains and a C-terminal RING domain. We show that at least one of these proteins is an intrinsic thylakoid membrane protein that fixes RPOTmp on the stromal side of the thylakoid membrane, probably via the RING domain. A model is presented in which light by triggering the synthesis of the RING protein determines membrane association and functional switching of RPOTmp.  a1091-6490