Nuclear and mitochondrial splice forms of human uracil-DNA glycosylase contain a complex nuclear localisation signal and a strong classical mitochondrial localisation signal, respectively

Abstract

Nuclear (UNG2) and mitochondrial (UNG1) forms of human uracil-DNA glycosylase are both encoded by the UNG gene but have different N-terminal sequences. We have expressed fusion constructs of truncated or site-mutated UNG cDNAs and green fluorescent protein cDNA and studied subcellular sorting. The unique 44 N-terminal amino acids in UNG2 are required, but not sufficient, for complete sorting to nuclei. In this part the motif R17K18R19is essential for sorting. The complete nuclear localization signal (NLS) in addition requires residues common to UNG2 and UNG1 within the 151 N-terminal residues. Replacement of certain basic residues within this region changed the pattern of subnuclear distribution of UNG2. The 35 unique N-terminal residues in UNG1 constitute a strong and complete mitochondrial localization signal (MLS) which when placed at the N-terminus of UNG2 overrides the NLS. Residues 11-28 in UNG1 have the potential of forming an amphiphilic helix typical of MLSs and residues 1-28 are essential and sufficient for mitochondrial import. These results demonstrate that UNG1 contains a classical and very strong MLS, whereas UNG2 contains an unusually long and complex NLS, as well as subnuclear targeting signals in the region common to UNG2 and UNG1.

The Hyper IgM Syndrome—An Evolving Story

“…Similar immunologic abnormalities as well as partially defective CSR and a bias pattern of SHM toward transitions at dG-dC nucleotides were reported in UNG-deficient mice (47). As in mice, human UNG has two promoters and two alternative splice products: the mitochondrial isoform, which is ubiquitously expressed, and the nuclear isoform, which is strongly expressed in proliferating cells (51,52). In each of the three patients, mutations were located in the catalytic domain of UNG.…”

Centromeres: The wild west of the post-genomic age

“…[91][92][93] UNG2 localizes to post-replication foci, 94 which overlap with centromeres transiently during G 2 . 46 Inhibiting UNG2 by multiple methods completely blocked CENP-A assembly.…”

Endogenous Expression of Activation-Induced Cytidine Deaminase in Cell Line WEHI-231

“…There are two splice variants, UNG1 and UNG2, which localize to the mitochondria and to the nucleus, respectively (36,37). The nuclear form, UNG2, takes part in class switching and hypermutation.…”