Structure and Expression of the TREX1 and TREX2 3′→5′ Exonuclease Genes

Abstract

The TREX1 and TREX2 genes encode mammalian 335 exonucleases. Expression of the TREX genes in human cells was investigated using a reverse transcription-polymerase chain reaction strategy. Our results show that TREX1 and TREX2 are expressed in all tissues tested, providing direct evidence for the expression of these genes in human cells. Potential transcription start sites are identified for the TREX genes using rapid amplification of cDNA ends to recover the 5-flanking regions of the TREX transcripts. The 5-flanking sequences indicate transcription initiation from consensus putative promoters identified ؊140 and ؊650 base pairs upstream of the TREX1 open reading frame (ORF) and ؊623 and ؊753 base pairs upstream of the TREX2 ORF. Novel TREX1 and TREX2 cDNAs are identified that contain protein-coding sequences generated from exons positioned in genomic DNA up to 18 kilobases 5 to the TREX1 ORF and up to 25 kilobases 5 to the TREX2 ORF. These novel cDNAs and sequences in the GenBank data base indicate that transcripts containing the TREX1 and TREX2 ORFs are produced using a variety of mechanisms that include alternate promoter usage, alternative splicing, and varied sites for 3 cleavage and polyadenylation. These initial studies have revealed previously unrecognized complexities in the structure and expression of the TREX1 and TREX2 genes.The multistep processes of DNA replication, repair, and genetic recombination often require the excision of 3Ј nucleotides to generate DNA 3Ј termini suitable for subsequent metabolic steps. The apparent diversity of proteins containing 3Ј 3 5Ј exonuclease activity likely reflects the different requirements for these enzymes in the maintenance of the human genome. In some cases these exonucleases are found in large proteins that contain multiple catalytic and functional properties. The 3Ј 3 5Ј proofreading exonucleases are functional domains in the mammalian DNA polymerases ␦ (1), ⑀ (2), and ␥ (3). These proofreading enzymes remove incorrectly polymerized nucleotides during DNA synthesis and minimize the incorporation of mismatches into the genome. The Werner syndrome protein (WRN) contains a 3Ј 3 5Ј exonuclease activity in one functional domain and a 3Ј 3 5Ј DNA helicase activity in another (4, 5). Deficiencies in the WRN protein increase genomic instability (6). The multifunctional p53 protein contains a 3Ј 3 5Ј exonuclease localized to the central core domain (7). This core region in p53 also contains the sequence-specific DNA binding domain that functions in cell-cycle checkpoint control in mammalian cells (8). The hRAD1 (Ustilago maydis REC1) and hRAD9 are human homologues of yeast DNA damage checkpoint response proteins (9). These proteins also contain 3Ј 3 5Ј exonuclease activities (10 -12). The yeast mre11 mutant is defective in recombinational DNA repair (13). The purified MRE11 protein (14, 15) and a protein complex containing MRE11 contain 3Ј 3 5Ј exonuclease activities (16). The TREX1 and TREX2 proteins are relatively small dimeric proteins that contain potent 3Ј 3 5Ј ...

Dominant Mutations of the TREX1 Exonuclease Gene in Lupus and Aicardi-Goutières Syndrome

“…No Enz, no enzyme. [3][4][5][6][7][8][9][10][11][12][13][14][15] and incubated with the nicked dsDNA plasmid. In these reactions, the catalytically inactive TREX1 D200H-containing enzymes compete with the TREX1 WT to bind the nicked dsDNA plasmid and inhibit degradation by TREX1…”

“…The TREX1 gene is a single open reading frame located on chromosome 3p21.31 (10). Mutations in the human TREX1 gene have been linked to a spectrum of autoimmune diseases including the severe neurological brain disease Aicardi-Goutières syndrome (AGS) 2 (11), to a monogenic form of cutaneous lupus erythematosus named "familial chilblain lupus" (FCL) (12)(13)(14), to systemic lupus erythematosus (15,16), and to retinal vasculopathy and cerebral leukodystrophy (17).…”

Early steps in the DNA base excision/single-strand interruption repair pathway in mammalian cells

“…TREX1 and TREX2 were identified as DNA 3′ exonucleases ubiquitously expressed in mammalian tissues [140,141]. Their primary function may be in editing during replication by Polb (and a) which lacks constitutive 3′ exonuclease activity.…”

The TREX1 Exonuclease R114H Mutation in Aicardi-Goutières Syndrome and Lupus Reveals Dimeric Structure Requirements for DNA Degradation Activity

“…TREX1 is the most abundant 3Ј35Ј exonuclease detected in mammalian cells and degrades both ssDNA 2 and dsDNA (1)(2)(3)(4). Deletion of the TREX1 gene in mice elicits an interferon-dependent autoimmune phenotype characterized by inflammatory myocarditis and a dramatically shortened lifespan (5)(6)(7).…”