One of the most fundamental processes within the cell is ensuring that translated proteins are compartmentalised to their appropriate location to ensure cell survival. To ensure that this process occurs correctly and efficiently, the cell employs several pathways to transport each protein to their designated area. There are two main transport systems for protein transport, which occur during (co-translational) or after (post-translational) the process of translation. These protein transport systems are highly characterised; however the protein complexes that mediate these pathways are not well understood. We are interested in the human ribonucleoprotein complex involved in the process of co-translational translocation known as the signal recognition particle (SRP), which is known to transport nascent proteins destined for the endoplasmic reticulum (ER) from the cytosol. To perform this function, the SRP has two functional domains known as the Alu and S domain, which are necessary for elongation arrest (Alu domain), recognition of the signal sequence and ER targeting (S domain).

In this complex we want to specifically understand the functions of the heterodimer, the signal recognition particle protein-68/72 (SRP68/72), which are two of the four proteins that comprise the S domain along with 7S RNA. Our aim is to understand its role in the complex during the process of co-translational translocation by firstly understanding its structure. Particularly, we want to crystallise the S domain, which is one of the domains that has yet to be fully explored. We also want to further understand how it binds to 7S RNA and to the SRP complex using electrophoretic mobility shift assays (EMSA) and microscale thermophoresis (MST). Currently, we have performed MST and/or EMSA to understand the protein-RNA interactions between a truncation of SRP72 and SRP68 to MiniS RNA, which contains the hypothesised binding region of SRP68/72. However, further analysis is required of the binding of SRP68 in conjunction with SRP72 onto 7S/MiniS RNA to fully understand the behaviour of the heterodimer.