Abstract
DNA replication initiates at genome sites termed origins. Previous origin mapping approaches in the populations of the protozoan parasite Leishmania major were discordant, suggesting either a single origin per chromosome or 200-fold more origins. To reconcile these data and fully understand DNA replication dynamics, we have applied DNAscent, an assay that detects patterns of 5-bromodeoxyuridine (BrdU) incorporation in individual long-read DNA molecules. We confirm the pre-eminence of a single locus of DNA replication initiation in each chromosome and reveal a much larger number of lower-efficiency DNA replication initiation events whose abundance is greater as chromosome size increases. Each initiation site is a region of high AT content, increased G-quadruplex levels, lowered chromatin occupancy, and reduced levels of nascent RNA. Finally, we show that all DNA replication initiation results in mutagenesis. This work reveals a bimodal strategy for DNA replication programming in Leishmania that drives replication timing and sequence variation.