Taxonomic distribution of proteins containing 35EXOc domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing 35EXOc domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Structures of normal single-stranded DNA and deoxyribo-3'-S-phosphorothiolates bound to the 3'-5' exonucleolytic active site of DNA polymerase I from Escherichia coli.

Brautigam CA, Sun S, Piccirilli JA, Steitz TA
Biochemistry. 1999; 38: 696-704

The interaction of a divalent metal ion with a leaving 3' oxygen is a central component of several proposed mechanisms of phosphoryl transfer. In support of this are recent kinetic studies showing that thiophilic metal ions (e.g., Mn2+) stimulate the hydrolysis of compounds in which sulfur takes the place of the leaving oxygen. To examine the structural basis of this phenomenon, we have solved four crystal structures of single-stranded DNA's containing either oxygen or sulfur at a 3'-bridging position bound in conjunction with various metal ions at the 3'-5' exonucleolytic active site of the Klenow fragment (KF) of DNA polymerase I from Escherichia coli. Two structures of normal ssDNA bound to KF in the presence of Zn2+ and Mn2+ or Zn2+ alone were refined at 2.6- and 2.25-A resolution, respectively. They serve as standards for comparison with other Mn2+- and Zn2+-containing structures. In these cases, Mn2+ and Zn2+ bind at metal ion site B in a nearly identical position to Mg2+ (Brautigam and Steitz (1998) J. Mol. Biol. 277, 363-377). Two structures of KF bound to a deoxyoligonucleotide that contained a 3'-bridging sulfur at the scissile phosphate were refined at 2.03-A resolution. Although the bridging sulfur compounds bind in a manner very similar to that of the normal oligonucleotides, the presence of the sulfur changes the metal ion binding properties of the active site such that Mn2+ and Zn2+ are observed at metal ion site B, but Mg2+ is not. It therefore appears that the ability of the bridging sulfur compounds to exclude nonthiophilic metal ions from metal ion site B explains the low activity of KF exonuclease on these substrates in the presence of Mg2+ (Curley et al. (1997) J. Am. Chem. Soc. 119, 12691-12692) and that the 3'-bridging atom of the substrate is influencing the binding of metal ion B prior to catalysis.

The proofreading domain of Escherichia coli DNA polymerase I and other DNA and/or RNA exonuclease domains.

Moser MJ, Holley WR, Chatterjee A, Mian IS
Nucleic Acids Res. 1997; 25: 5110-8

Prior sequence analysis studies have suggested that bacterial ribonuclease (RNase) Ds comprise a complete domain that is found also in Homo sapiens polymyositis-scleroderma overlap syndrome 100 kDa autoantigen and Werner syndrome protein. This RNase D 3'-->5' exoribonuclease domain was predicted to have a structure and mechanism of action similar to the 3'-->5' exodeoxyibonuclease (proofreading) domain of DNA polymerases. Here, hidden Markov model (HMM) and phylogenetic studies have been used to identify and characterise other sequences that may possess this exonuclease domain. Results indicate that it is also present in the RNase T family; Borrelia burgdorferi P93 protein, an immunodominant antigen in Lyme disease; bacteriophage T4 dexA and Escherichia coli exonuclease I, processive 3'-->5' exodeoxyribonucleases that degrade single-stranded DNA; Bacillus subtilis dinG, a probable helicase involved in DNA repair and possibly replication, and peptide synthase 1; Saccharomyces cerevisiae Pab1p-dependent poly(A) nuclease PAN2 subunit, required for shortening mRNA poly(A) tails; Caenorhabditis elegans and Mus musculus CAF1, transcription factor CCR4-associated factor 1; Xenopus laevis XPMC2, prevention of mitotic catastrophe in fission yeast; Drosophila melanogaster egalitarian, oocyte specification and axis determination, and exuperantia, establishment of oocyte polarity; H.sapiens HEM45, expressed in tumour cell lines and uterus and regulated by oestrogen; and 31 open reading frames including one in Methanococcus jannaschii . Examination of a multiple sequence alignment and two three-dimensional structures of proofreading domains has allowed definition of the core sequence, structural and functional elements of this exonuclease domain.

Compilation, alignment, and phylogenetic relationships of DNA polymerases.

Braithwaite DK, Ito J
Nucleic Acids Res. 1993; 21: 787-802

Structure of large fragment of Escherichia coli DNA polymerase I complexed with dTMP.

Ollis DL, Brick P, Hamlin R, Xuong NG, Steitz TA
Nature. 1985; 313: 762-6

The 3.3-A resolution crystal structure of the large proteolytic fragment of Escherichia coli DNA polymerase I complexed with deoxythymidine monophosphate consists of two domains, the smaller of which binds zinc-deoxythymidine monophosphate. The most striking feature of the larger domain is a deep crevice of the appropriate size and shape for binding double-stranded B-DNA. A flexible subdomain may allow the enzyme to surround completely the DNA substrate, thereby allowing processive nucleotide polymerization without enzyme dissociation.