Fig. 2. Identification of psm cluster products produced in the presence of the PsmK kinase. MALDI-MS spectra of E. coli cells harboring control empty vector plasmids (upper panel), plasmids expressing the psm cluster without the psmK gene (psmCAB1B2ND) or cells expressing the mutated cluster and harboring an additional plasmid expressing wild-type or D158A D159A double mutant psmK (psmK*). Mass-peaks that are common to both control and experimental cells are indicated by black-color font. The average m/z values of mass-peaks of psm cluster products are highlighted with red-color font (see text for details).