sentence: If RNA is in hybrid with DNA in bona fide replication intermediates in vivo , cross-linking should protect it from digestion by RNase H. Conversely , if the RITOLS-type intermediates arise as an artifact during extraction , due to hybridization of mitochondrial RNA to a displaced parental DNA strand after protease treatment , the RNA will remain RNase H sensitive after in vivo cross-linking.When intact rat liver mitochondria ( Figure 1 , Supplementary Figure S1B ) or tissue homogenates ( Supplementary Figure S1C ) were treated with psoralen before mtDNA extraction , mtRIs proved markedly more resistant to RNase H than those of controls , when analyzed by 2D-AGE after digestion with BspHI .