Disease relevance of tos

• POLN has a processivity of DNA synthesis (1-100 nucleotides) similar to the exonuclease-deficient Klenow fragment of E. coli pol I, is inhibited by dideoxynucleotides, and resistant to aphidicolin [1].

Psychiatry related information on tos

• Instead, 3'-terminal mispairs are hydrolyzed quantitatively by the 3'-->5' exonuclease over the reaction time course [2].

High impact information on tos

• An exonuclease protection assay reveals heat-shock element and TATA box DNA-binding proteins in crude nuclear extracts [3].
• Recently, two protein-binding (exonuclease-resistant) sites which cover the TATA box sequence and an upstream control element were shown to occur in vivo amidst the 5' terminal hypersensitive regions of several heat shock genes [4].
• These results suggest that the 3'----5' exonuclease functions as a proofreading enzyme during Drosophila DNA replication in vitro and very likely in vivo [5].
• However, a potent exonuclease can be detected after separating the 182-kDa polymerase subunit from the other three subunits of the enzyme (73, 60, and 50 kDa) by glycerol gradient sedimentation in the presence of 50% ethylene glycol [5].
• Factors were detected in both types of extracts that block exonuclease digestion from a downstream site at ca. +35 and -20 base pairs from the start of transcription of all four of these promoters [6].

Biological context of tos

• The definite oocyte localization of tos transcript during meiosis and its ubiquitous distribution in early embryos suggest that tos may play a role in mismatch repair during genetic recombination and early cleavage divisions [7].
• In the early embryo, the maternally supplied tos mRNA is evenly distributed at the syncytial blastoderm stage, but is excluded from the forming cells when cellularization begins. tos product is the first Drosophila member of the RAD2 protein family, a group of related DNA repair nucleases conserved from yeast to humans [7].
• Within the family, Tos is more closely related to ExoI, a Schizosaccharomyces pombe 5'-->3' double-stranded DNA exonuclease specifically induced in meiotic prophase I [7].
• We describe here a Drosophila gene, tosca (tos), that is specifically expressed in the female germline. tos mRNA accumulates selectively within the pro-oocyte in germarial region 2 and persists throughout oogenesis [7].
• In addition, factors in extracts from heat-shocked embryos blocked exonuclease digestion at sites flanking the heat shock consensus sequences of hsp26 and hsp70 [6].

Anatomical context of tos

• The polymerase-primase complex from calf thymus exhibited no detectable 3'----5' exonuclease activity using a heteroduplex substrate containing a single 3'-terminal mismatched nucleotide [8].
• In eukaryotic cells degradation of bulk mRNA in the 5' to 3' direction requires the consecutive action of the decapping complex (consisting of DCP1 and DCP2) and the 5' to 3' exonuclease XRN1 [9].

Associations of tos with chemical compounds

• To determine the specificity of excision of mispaired nucleotides by the exonuclease, we have utilized primed phi X174am3 single-stranded DNA containing a noncomplementary nucleotide at the 3'-primer terminus, opposite deoxyadenosine at position 587 in the amber3 codon of the template strand [10].
• 3'-->5' exonuclease in Drosophila mitochondrial DNA polymerase. Substrate specificity and functional coordination of nucleotide polymerization and mispair hydrolysis [2].

Other interactions of tos

• DmGEN, a novel RAD2 family endo-exonuclease from Drosophila melanogaster [11].
• This polymerase shared some common properties with DNA polymerase epsilon from mammals and yeast as follows; it has a preference for poly(dA)/oligo(dT) as a template/primer, it is highly processive in DNA synthesis, it co-fractionates with 3'-5' exonuclease activity, it is sensitive to aphidicolin and is resistance to ddTTP [12].
• Chromatin at the Drosophila Adh distal promoter displays an ordered but different conformation in different cell types as detected by a modified exonuclease protection assay and accessibility to endonucleases [13].

References