The effort for preparing this review was supported by the Office of Science, Office of Biological and Environmental Research, of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231 through ENIGMA -Ecosystems and Networks Integrated with Genes and Molecular Assemblies (http://enigma.lbl.gov), a Scientific Focus Area Program at Lawrence Berkeley National Laboratory and the Oklahoma Applied Research Support (OARS), Oklahoma Center for the Advancement of Science and Technology (OCAST), the State of Oklahoma through the Project AR062-034. Functional Studies of ssDNA Binding Ability of MarR Family Protein TcaR from Staphylococcus epidermidis The negative transcription regulator of the ica locus, TcaR, regulates proteins involved in the biosynthesis of poly-N-acetylglucosamine (PNAG). Absence of TcaR increases PNAG production and promotes biofilm formation in Staphylococci. Previously, the 3D structure of TcaR in its apo form and its complex structure with several antibiotics have been analyzed. However, the detailed mechanism of multiple antibiotic resistance regulator (MarR) family proteins such as TcaR is unclear and only restricted on the binding ability of double-strand DNA (dsDNA). Here we show by electrophoretic mobility shift assay (EMSA), electron microscopy (EM), circular dichroism (CD), and Biacore analysis that TcaR can interact strongly with single-stranded DNA (ssDNA), thereby identifying a new role in MarR family proteins. Moreover, we show that TcaR preferentially binds 33-mer ssDNA over double-stranded DNA and inhibits viral ssDNA replication. In contrast, such ssDNA binding properties were not observed for other MarR family protein and TetR family protein, suggesting that the results from our studies are not an artifact due to simple charge interactions between TcaR and ssDNA. Overall, these results suggest a novel role for TcaR in regulation of DNA replication. We anticipate that the results of this work will extend our understanding of MarR family protein and broaden the development of new therapeutic strategies for Staphylococci. Staphylococci are among the most common causes of bacterial infection in the community and pose a major danger to human health. S. aureus is the most well-known of the species which produce hospital-and community-acquired infections, with methicillin-resistant S. aureus presenting a serious public health threat [1] . S. epidermidis is the sister species of S. aureus which often causes infection in immunocompromised individuals or those following damage to the epithelium. Both of them produce biofilm to protect themselves from host immune system and enhance their resistance to antibiotic chemotherapy [2] . The key component of the biofilm extracellular matrix in Staphylococci is polysaccharide intercellular adhesin (PIA) [3] , an essential factor in biofilm formation composed of homopolymer of b-1,6-linked N-acetylglucosamine (GlcNAc). The production of PIA depends on the expression of the icaADBC operon, and TcaR and IcaR are a weak and a strong negative regulator of transcription of the ica locus, respectively [4] .