Cover photograph (Copyright © 2008, American Society for Microbiology. All Rights Reserved.): Mycobacterium smegmatis SigF, Persian carpet style. The motif is a repeated image of a petri dish containing wild-type M. smegmatis, the sigF mutant, and the complemented strain. The background corresponds to a thin-layer chromatograph of the carotenoid pigments. (See related article on page 7859.)