Proteomic survey of the Streptomyces coelicolor nucleoid

Nucleoid-associated proteins (NAPs) are small, highly abundant regulators with low sequence specificity and pleiotropic mutant phenotypes. They are involved in transcriptional and post-transcriptional control of gene expression, DNA protection/repair and nucleoid structuring. Discovery of the major NAPs has been largely haphazard and based with the Enterobacteriaceae, although some Actinomycete-specific NAPs (Mdp1, Lsr2, sIHF) are known. Here, we use LC-MS/MS to systematically search for novel NAPs in isolated nucleoids of the model actinomycete Streptomyces coelicolor. Based on the criteria of high abundance (emPAI) and predicted DNA-binding ability (DNAbinder) we identified a set of around twenty proteins with a good probability of being NAPs. The approach was apparently successful as the set included known major NAPs HupA, sIHF and Lsr2 as well as the global regulators BldD and CRP. It also included a number of proteins whose functions are not yet known (SCO0204, SCO3013, SCO4232, SCO4199 and SCO1839) which provide a useful set of candidates for further study.