Replication of Kinetoplast DNA

Abstract

Kinetoplast DNA is the mtDNA of trypanosomatids. Trypanosomatids are parasitic protozoa, and some members of this family are responsible for major tropical diseases that afflict millions of people in many developing countries. Each trypanosomatid cell contains only a single mitochondrion, and the kinetoplast DNA resides within the matrix of this mitochondrion. Kinetoplast DNA has a remarkable structure. It consists of thousands of DNA circles that are joined together, presumably by interlocking, in a single massive network (Fig. 1). The circles are of two types. Minicircles are the major component and they make up about 95% of the mass of the network. They range in size from about 0.8 kb to 2.5 kb, depending on the species, and within a network the minicircles are usually heterogeneous in sequence. Maxicircles comprise only about 5% of the mass of the network. They range in size from about 20 kb to 38 kb, depending on the species, and within a network they are homogeneous in sequence. Maxicircles carry genes similar to those found in mtDNA in other eukaryotes. The function of minicircles, however, and the reason for the network structure are not yet known. (For reviews on kinetoplast DNA, see Simpson [1972]; Hajduk [1978]; Borst and Hoeijmakers [1979a]; Barker [1980]; and Englund [1981].)

During the past several years we have studied the replication of kinetoplast DNA. In this process the single network within a mitochondrion replicates to form two identical networks, which are then segregated into the daughter cells. Replication involves not only the...