Wheat DNA polymerase CI: a homologue of rat DNA polymerase beta

We have previously described a low-molecular-weight DNA polymerase (52 kDa) from wheat embryo: DNA polymerase CI (pol CI). This enzyme shares some biochemical properties with animal DNA polymerase beta (pol beta). In this report, we analyse pol CI in wheat embryo germination. Immunodetection and measurement of the enzyme activity show that wheat pol CI remains at a constant level during germination, whereas dramatic changes of the replicative DNA polymerase A and B activities were previously reported. We observe that the level of pol CI in physiological conditions (embryo germination and dividing cell culture) is in agreement with a pol beta-type DNA polymerase. By microsequencing of the electroblotted 52 kDa polypeptide, we determined the sequence of a dodecapeptide from the N-terminal region. A comparative analysis of the N-terminal pol CI peptide with some mammalian pol beta sequences shows a clear homology with helix 1 of the N-terminal ssDNA domain (residues 15 to 26) of the rat pol beta. Thus, the helical structure of this region should be conserved in the wheat peptide. This represents the first evidence of a partial primary structure of a beta-type DNA polymerase in plants.