DNA-protein interactions in theDrosophila virilismitochondrial chromosome

The location of proteins on the mitochondrial DNA (mtDNA) of Drosophila virilis was investigeted by Me 3 peoralen photoreaction of mitochondria isoleted from embryos. After photoreaction the mtDNA was purified and the pattern of DNA cross-linking was determined by electron microscopy of the DNA under totally denaturing conditions. The transcribed regions of the mtDNA molecule contained aome uncross-linked regions, but auch regions were infrequent and randomly distributed. In contrast, the A+T-rich region around the origin of replication of the mtDNA was usually protected from psoralen crosslinking. The data were best fit by two protected sites, each approximately 400 base pairs, compared to the four 400 base pair sites observed in the equivalent region of D . melanogester mtDNA Potter et al. (1980) Proc. Nat. Acsd. Sci. USA 77, 4118−4122. Thus this region of the mtDNA appears to be involved in a DNA-protein structure that is highly conserved even though the DNA sequence has diverged rapidly relative to protein-coding sequences.