INTEGRATION OF A CYANOBACTERIAL PROTEIN INVOLVED IN NITRATE REDUCTION(NARB) INTO ISOLATED SYNECHOCOCCUS BUT NOT INTO PEA THYLAKOID MEMBRANES

Chimeric genes comprised of Rubisco small subunit transit peptide fuse d in frame with full-length and truncated sequences of a nitrate reduc tase (narB) structural gene of Synechococcus were constructed. Fusion proteins were synthesized in a rabbit reticulocyte system. In thylakoi do integration of synthetic proteins resulted in the association of th e full-length narB-coded protein to the Synechococcus photosynthetic m embranes. The membrane-associated protein was sensitive to trypsin tre atment but could not be removed by washing in the presence of NaBr. Tr ypsin pretreatment of thylakoids abolished the capability for associat ion. The association of the narB-coded protein with thylakoids might r equire another membrane protein whose identity is not known. It is pro posed that the Synechococcus narB polypeptide is a peripheral, membran e bound protein anchored to the thylakoids via a short hydrophobic dom ain while the major part of the protein resides on the outer side of t he thylakoid membranes. The chimeric narB proteins were processed and imported by intact pea chloroplasts in vitro; however, the mature prot eins were found localized in the stroma and not in the thylakoid membr ane fraction. Similarly, the attempt to integrate the protein in vitro into isolated pea thylakoid membranes failed although these membranes incorporate early light-inducible proteins.