Detection of large non-circular forms of the chromosome by pulsed-field gel electrophoresis. AB1157 (= rec+) and JC5519 (= recBC) cells were grown either in M9, a minimal medium, or in LB, a rich broth (Materials and Methods). The cells were harvested, embedded in agarose, lysed in situ, and analyzed by pulsed-field gel electrophoresis. Giant circular chromosomes stay in the well. Huge non-circular forms generated by ds breakage will band just below the well (bar in the right). Lane "M" contains Saccharomyces cerevisiae chromosomes as linear size markers.