WHEAT DNA-POLYMERASE CI - A HOMOLOG 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 share s some biochemical properties with animal DNA polymerase beta (pol bet a). In this report, we analyse pol CI in wheat embryo germination. Imm unodetection and measurement of the enzyme activity show that wheat po l CI remains at a constant level during germination, whereas dramatic changes of the replicative DNA polymerase A and B activities were prev iously reported. We observe that the level of pol CI in physiological conditions (embryo germination and dividing cell culture) is in agreem ent with a pol beta-type DNA polymerase. By microsequencing of the ele ctroblotted 52 kDa polypeptide, we determined the sequence of a dodeca peptide from the N-terminal region. A comparative analysis of the N-te rminal pol CI peptide with some mammalian pol beta sequences shows a c lear 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 regio n 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.