Signal recognition particles (SRPs) in pro- and eukaryotes function in cotranslational targeting of nascent poplypeptides to an SRP receptor at the target membrane. A unique chloroplast SRP (cpSRP) functions post-translationally to direct light-harvesting chlorophyll-binding proteins (LHCPs) to the receptor cpFtsY at the thylakoid membrane for LHCP insertion in a process involving the integral membrane protein Albino3 (Alb3) and requiring GTP. Work here focuses on understanding cpSRP targeting events at the thylakoid membrane, specifically those involving Alb3 and the lipid environment.

We show an interaction between the novel cpSRP subunit cpSRP43 and the soluble, stromal-exposed C terminus of Albino3 (Alb3-Cterm). We determine that the site for this interaction is housed in an ankyrin repeat region of cpSRP43. Further, we provide functional relevance to this interaction within the overall targeting pathway. We also examine the role of lipids in cpSRP targeting and show the ability of artificial liposomes to support critical cpSRP functions. Work was also done in creating thylakoidmimicking liposomes and using various microscopy techniques to visualize targeting components in a lipid environment. Finally, we report an interaction between Alb3 and the Arabidopsis thaliana large ribosomal subunit protein L23, which hints at a cotranslational function for Alb3.