Elongation of displacement-loop strands in human and mouse mitochondrial DNA is arrested near specific template sequences.

Abstract

Animal mitochondrial [mt] DNA maintains a displacement loop (D loop) at the heavy strand origin of replication. These D loops represent sharply limited synthesis of heavy strands and provide a unique opportunity to examine the termination of DNA synthesis. Direct sizing at the nucleotide level indicates that the 3'' ends of D-loop strands of human and mouse mtDNA are discrete and map within 3-5 nucleotides on the complementary template strand. In the case of human mtDNA, there is a single trinucleotide stop point 51-53 nucleotides downstream from a 15-nucleotide template sequence (3''T-A-A-C-C-C-A-A-A-A-A-T-A-C-A 5'') which is repeated 4 times in the mouse mtDNA D loop region 3''(T-A-A-Py-Py-A-A-A-T-T-A-C-A 5''). The stop points of the 5 major mouse D-loop strands are 24-63 nucleotides downstream from the 4 repeated template sequences. The arrest of D-loop strand elongation is an event determined by template sequence.