Masses of polypeptides associated with gltB DNA in vitro. Surface-enhanced laser desorption and ionization (SELDI; Ciphergen Biosystems) was used to identify proteins from whole-cell E. coli extracts binding to biotin-labeled gltB DNA (from -406 to +246). The DNA was attached to streptavidin-coated chips, incubated with the extracts, and washed prior to mass analysis. Parts A and B show different mass ranges. The vertical arrows indicate the theoretical positions of the indicated polypeptides; in each case the mass shown assumes removal of the N-terminal methionine.