Table 6.
Biochemically active DNA helicases from plant cells. CDH, Chloroplast DNA helicase; DSBs, double‐strand breaks; HDH, human DNA helicase; nd, not determined; PDH, pea DNA helicase.
| S. No. | Name of helicase | Mol. mass (kDa) | Nucleotide cofactors | Polarity | Remarks |
|---|---|---|---|---|---|
| 1. | Lily U‐protein a | 130 (native) | ATP | nd | Partially purified. Unwinds DNA from ends, gaps and nicks. Its abundance increases during meiosis. |
| 2. | Soybean chloroplast DNA helicase b | nd | ATP ≫ GTP > dATP > NTPs | nd | Partially purified. Shows unwinding activity at higher conc. of Mg2+ (10 mm). |
| 3. | Pea chloroplast DNA helicase I (CDH I) c | 68 138 (native) | ATP > dATP ≫ NTPs | 3′−5′ | First plant helicase reported in purified form. It is a homodimer. |
| 4. | Pea chloroplast DNA helicase II (CDH II) d | 78 | ATP = dATP | 3′−5′ | Purified to homogeneity. Stimulated by fork‐like structures. |
| 5. | Pea nuclear DNA helicase I (PDH45) e | 45 | ATP > dATP ≫ NTPs | 3′−5′ | First plant nuclear DNA helicase; homologous to eIF‐4 A; stimulates topo I activity. |
| 6. | Pea nuclear DNA helicase II (PDH65) f | 65 | ATP > dATP | 3′−5′ | A plant homolog of HDHI. localized in nucleo lus. Phosphorylated and upregulated by CK2 and cdc2 protein kinases. |
| 7. | Arabidopsis Ku DNA helicase (AtKu70/80) g | 70.3 76.7 | ATP | nd | Functions as heterodimer that binds to dsDNA. Gene expression is induced by DSBs, may be involved in DSB repair. |
| 8. | Pea nuclear DNA helicase III (PDH120) h | 54 66 120 (native) | ATP > NTPs | 3′−5′ | Purified to homogeneity. Present at extremely low abundance and contain the high specific activity. |