Cover photograph (Copyright © 2004, American Society for Microbiology. All Rights Reserved.): Novel strategy for rapid megabase pair scanning for enhancers in founder transgenic mice. Four “BAC-trap” transgenic mice display lacZ expression in organs and tissues containing enhancers encoded within overlapping domains, and only one (top left) contains transcription factor GATA-2 urogenital activity. (See related article on p. 10263.)