title: Identification of chloroplast signal recognition particle RNA genes.
abstract: The signal recognition particle (SRP) is a ribonucleoprotein complex responsible for targeting proteins to the ER membrane in eukaryotes, the plasma membrane in bacteria and the thylakoid membrane in chloroplasts. In higher plants two different SRP-dependent mechanisms have been identified: one post-translational for proteins imported to the chloroplast and one co-translational for proteins encoded by the plastid genome. The post-translational chloroplast SRP (cpSRP) consists of the protein subunits cpSRP54 and cpSRP43. An RNA component has not been identified and does not seem to be required for the post-translational cpSRP. The co-translational mechanism is known to involve cpSRP54, but an RNA component has not yet been identified. Several chloroplast genomes have been sequenced recently, making a phylogenetically broad computational search for cpSRP RNA possible. We have analysed chloroplast genomes from 27 organisms. In higher plant chloroplasts, no SRP RNA genes were identified. However, eight plastids from red algae and Chlorophyta were found to contain an SRP RNA gene. These results suggest that SRP RNA forms a complex in these plastids with cpSRP54, reminiscent of the eubacterial SRP.
authors.affiliation: Department of Medical Biochemistry, Goteborg University, Box 440, SE-405 30 Goteborg, Sweden.
authors.forename: Magnus Alm
authors.initials: MA
authors.lastname: Rosenblad
authors.forename: Tore
authors.initials: T
authors.lastname: Samuelsson
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002736:Chloroplasts / Q000235:genetics*; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010802:Phylogeny; D018747:RNA, Chloroplast / Q000235:genetics*; D018271:Signal Recognition Particle / Q000235:genetics*; D026801:Synteny
chemical_list: D018747:RNA, Chloroplast; D018271:Signal Recognition Particle