Targeting of newly synthesized membrane proteins to the endoplasmic reticulum is an essential cellular process. Most membrane proteins are recognized and targeted co-translationally by the signal recognition particle (SRP). However, nearly 10% of membrane proteins belong to the tail-anchored (TA) family and are not handled by the SRP system. During the biosynthesis of tail-anchored (TA) membrane proteins, their single C-terminal trans-membrane segment is inserted into the ER membrane for orientating the functional domain(s) towards the cytosolic side of the cell. The machinery responsible for this post-translational process has only recently come to light. In yeast, the newly characterized Get pathway (Guided Entry of Tail-anchored protein) is the major targeting pathway for TA proteins in yeast including Get1, Get2, Get3, Get4 and Get5. In addition, Mass spectrometry and yeast two-hybrid assays indicate that these Get proteins, along with a tetratricopeptide repeat-containing protein called Sgt2, all interact with one another in some fashion. In order to elucidate the detail machinery of TA protein targeting to ER, we study the communicating manner among these GET members by using X-ray crystallography with several biophysical and biochemical experiments.
Complete and faithful replication of the genome requires the ability of cells to respond to DNA damage. Under normal growth conditions, replication forks formed at the bacterial origin of replication, oriC, frequently encounter sites of DNA damage that can result in their inactivation. These stalled replication forks must be efficiently repaired to allow replication of the genome to resume. Processes that reinitiate replication at repaired forks thus represent major housekeeping functions in bacteria that are essential for viability. In E. coli, a number of proteins, collectively referred to as the primosome, are responsible for reactivating repaired replication forks. There are seven proteins comprising the primosome, PriA, PriB, PriC, DnaT, DnaB, DnaC, and DnaG. In this project, we study the structure and function of these components of primosomal proteins.