Showing papers by "Joan C. Marini published in 1982"

Bent helical structure in kinetoplast DNA.

Abstract: We have investigated the unusual physical properties of a restriction fragment of Leishmania tarentolae kinetoplast DNA. A gel-purified fragment comprising slightly more than half of a minicircle was determined by Maxam-Gilbert sequence determination to be 490 base pairs (bp) in length. This fragment has dramatically anomalous electrophoretic behavior; it has an apparent size of 450 bp on a 1% agarose gel but migrates as 1,380 bp on a 12% polyacrylamide gel. However, in gel filtration on Sephacryl S-500, the fragment elutes with an apparent size of 375 bp. Finally, it behaves anomalously in electric dichroism experiments. Field-free rotational relaxation times from transient electric dichroism studies are highly sensitive to effective molecular dimensions. The rotational relaxation time of the kinetoplast fragment is smaller than that of a 309-bp control fragment from pBR322. Because rigorous control experiments rule out the possibility that this fragment is modified, these anomalous properties must be dictated by the sequence itself. Fragment behavior indicates that it has an unusually compact configuration; we propose that this molecule contains a region of systematically bent B-DNA. This model accounts for the fragment's difficulty in snaking through the pores of a polyacrylamide gel, its ease in diffusing into Sephacryl beads, and its smaller rotational relaxation time. Bending of this molecule may be caused by periodicities in the DNA sequence.

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...