Isolation, purification and function analysis of an HNH domain containing nuclease from maize pollen
Hui Qi, Quan Zhang and Sodmergen^*

Key Laboratory of Ministry of Education for Cell Proliferation and Differentiation, College of Life Sciences, Peking University, Beijing 100871, China.
^*Correponding author: Email, sodmergen@pku.edu.cn

Abstract
DNA (including nuclear DNA and cytoplasmic DNA) in plant cell are not in a static state. The amounts of DNA were adjusted during development and tissue differentiation, and nuclease is indispensable in these processes. Here a 20kD HNH domain containing nuclease, M20 was purified from mitochondria of maize pollen. M20 was a thermally stable and Mg²⁺ or Mn²⁺-dependent endonuclease, which can non-specifically hydrolyze the salmon sperm genomic DNA and the circular plasmid PUC18 in vitro. As previous characterized HNH domain containing proteins, M20 had three conserved amino acids that are necessary for the hydrolytic activity. The differences between the native molecular weight on Gel filtration and the denaturing SDS-PAGE electrophoresis demonstrated that M20 may exist as a dimer in non-denaturing system. For the homologue of M20 in Arabidopsis, AtM20, no efficient T-DNA insertion line was emerged. The transcriptional level of AtM20 was partial reduced in the RNAi and amiRNA transgenic plants, but no visible defect was detected. AtM20 expressed mainly in early mature pollen, which indicates M20 may play a role in pollen development.

Key Words: HNH domain, maize pollen, mitochondria, nuclease