Expression of a maize δ‐type DNA polymerase during seed germination

Abstract

We have cloned a 1563‐bp cDNA sequence from a reported 2072‐bp cDNA (including a fragment of the 3′ UTR region, accession number AY109773) corresponding to the carboxy half of maize DNA polymerase δ[Zea mays delta‐type DNA polymerase catalytic subunit (Zmpolδ); EC 2.7.7.7], and its sequence shows an identity of 95, 77 and 74% to rice, soybean and Arabidopsis enzymes, respectively, although identity is even higher if only the polδ‐defining domain sequences are considered. An important difference between the monocot and dicot enzymes is the presence in the former of Zn fingers apparently required for binding to the DNA polδ holoenzyme B subunit, which is absent in the dicot enzymes. Expression of Zmpolδ and protein levels during germination remain unchanged; however, polδ shows two peaks of activity, one during early germination, perhaps related to DNA repair processes and a second peak when DNA replication is already in progress, indicating that Zmpolδ is regulated at the post‐translational level. Zmpolδ has been found mainly in proliferative tissues in seeds and plantlets, although surprisingly, it is also present in seed endosperm, together with Zm proliferating cell nuclear antigen.