Electrospray mass spectrometry of gas phase macromolecular complexes
Recent work involving the use of electrospray ionization mass spectrometry to study protein-DNA complexes is reviewed. In particular, our on-going work involving complexes in the bacterial replisome, a giant nucleoprotein complex that faithfully copies DNA during replication of the chromosome, is presented. We have examined different complexes important in DNA replication in E. coli, each with different binding modes. Results for two complexes studied to date (i) Tus protein (35,652 Da), with its double-stranded 21 mer DNA recognition sequence, Ter B; and (ii) the protein-protein complex formed between the theta and epsilon subunits of DNA polymerase III (i.e., a multisubunit enzyme that is the major replicative polymerase of E. coli) are presented here. ESI-MS studies of both these complexes have provided new information concerning the nature of the binding and enabled us to investigate the limitations and advantages of studying such complexes in the gas phase.