Plastid DNA polymerases

Eukaryotic cellular template-dependent DNA polymerases can be classified into a, ß, y, 8, and e DNA polymerases based largely on work in vertebrates and yeast (Wang 1991). The a, ß, 8, and e DNA polymerases are located in nuclei whereas the y-DNA polymerase is located in mitochondria. This original list of five eukaryotic DNA polymerases has expanded to fourteen (Mori et al. 2005) as new DNA polymerases are identified including those involved in translesion DNA synthesis (Hubscher et al. 2000). Nine classes of DNA polymerase have been identified by analyses of plant genomes (Mori et al. 2005). The activity of y-DNA polymerases is resistant to aphidicolin, sensitive to N-ethylmaleimide, and relatively resistant to low concentrations of dideoxynucleoside 5' triphosphates (Wang 1991). This y-DNA polymerase activity can be distinguished from a, 8, and e DNA polymerases which are sensitive to aphidicolin but resistant to dideoxynucleoside 5' triphosphates, and ß-DNA polymerase, which is resistant to both aphidocolin and N-ethylmaleimide but sensitive to low concentrations of dideoxynucleoside 5' triphosphates (Wang 1991). Plastid DNA polymerases that have been characterised from S. oleracea (Spencer and Whitfeld 1969; Sala et al. 1980), P. sativum (McKown and Tewari 1984), G. max (Heinhorst et al. 1990; Bailey et al. 1995), N. tabacum (Sakai et al. 1999), and C. reinhardtii (Wang et al. 1991) resemble y-DNA polymerases based on their resistance to aphidocolin and sensitivity to N-ethylmaleimide. Furthermore, the plant but not the C. reinhardtii plastid DNA polymerases are resistant to low concentrations of dideoxynucleoside 5' triphosphates (Heinhorst and Cannon 1993). The activities of purified plastid DNA polymerases appear to be stimulated by KCl (Spencer and Whitfeld 1969; Sala et al. 1980; McKown and Tewari 1984; Heinhorst et al. 1990; Sakai et al. 1999) and inhibited by ethidium bromide (McKown and Tewari 1984; Wang et al. 1991; Sakai et al. 1999).

Estimated sizes of plastid DNA polymerases were 87 kDa (McKown and Tewari 1984) and 70 kDa for P. sativum (Gaikwad et al. 2002), 85-90 kDa for G. max (Heinhorst et al. 1990), 116 kDa for N. tabacum (Sakai et al. 1999), and

Table 2. Plastid DNA-RRR proteins encoded by Arabidopsis thaliana nuclear genes.

Protein

Length (aa)

Acc. no.

Gene no.

Reference

DNA poly-

10491

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