Department of Microbiology, University of Massachusetts, Amherst, MA 01003, USA. klingbeil@microbio.umass.edu
In this issue, Liu et al. (2009) report that maxicircle DNA copy number in trypanosomes is regulated by proteolysis of a helicase; the complex kinetoplast DNA system yields a clear view of how mitochondrial DNA replication can be regulated.