Transient interaction of cpSRP54 with elongating nascent chains of the chloroplast-encoded D1 protein; 'cpSRP54 caught in the act'.
The signal recognition particle (SRP) in bacteria and endoplasmic reticulum is involved in co-translational targeting. Plastids contain cpSRP54 and cpSRP43, unique to plants, but lack a SRP RNA molecule. A role for cpSRP in biogenesis of plastid-encoded membrane proteins has not been firmly established yet. In this study, a transient interaction between cpSRP54 and elongating D1 protein was observed using a homologous chloroplast translation system. Using the novel approach of cross-linking at different time points during elongation of full-length D1 protein, we showed that cpSRP54 interacts strongly with the elongating nascent chain forming two distinct cross-linked products. However, this interaction did not lead to an elongation arrest and cpSRP54 was released from the nascent chains, once they were longer than approximately 14 kDa. Detailed mutant analysis showed that the cpSRP54 interaction occurred via the first transmembrane domain, which could be replaced by other hydrophobic domains of more than 10 amino acids.
Nilsson
Robert
R
Department of Plant Biology, Cornell University, Ithaca, NY 14853, USA.
van Wijk
Klaas Jan
KJ
D002736:Chloroplasts / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045332:Photosystem II Protein Complex; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle / Q000378:metabolism*
D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; C069268:SRP54 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D018271:Signal Recognition Particle