Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.7 (DNA polymerase)
 17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The proposal that Ap4A acts as an inducer of DNA replication is based primarily on two pieces of evidence (7). The intracellular levels of Ap4A increase ten- to 1000-fold as cells progress into S phase and the introduction of Ap4A into nonproliferating cells stimulated DNA synthesis. There is also some additional suggestive evidence such as the binding of Ap4A to a protein that is associated with multiprotein forms of the replicative DNA polymerase alpha and the ability of this enzyme to use Ap4A as a primer for DNA synthesis in vitro with single-stranded DNA templates. These observations have stimulated interest in the cellular metabolism of Ap4A. This is well since there is a great need for additional experimentation in order to clearly establish Ap4A as an inducer of DNA replication. Microinjection experiments of Ap4A into quiescent cells are needed in order to ascertain if Ap4A will stimulate DNA replication and possibly cell division in intact cells. Studies of the effects of nonhydrolyzable analogs of Ap4A on DNA replication in intact quiescent cells could also prove valuable. Although Ap4A can function as a primer for in vitro DNA synthesis by DNA polymerase alpha this may not be relevant in regard to its in vivo role in DNA replication. Ap4A in vivo could interact with key protein(s) in DNA replication and in this way act as an effector molecule in the initiation of DNA replication. In this regard the interaction of Ap4A with a protein associated with a multiprotein form of DNA polymerase alpha isolated from S-phase cells is of interest. More experiments are required to determine if there is a specific target protein(s) for Ap4A in vivo and what its role in DNA replication is. The cofractionation of tryptophanyl-tRNA synthetase with the replicative DNA polymerase alpha from animal and plant cells is of interest. The DNA polymerase alpha from synchronized animal cells also interacted with Ap4A. Although the plant cell alpha-like DNA polymerase did not interact with Ap4A this DNA polymerase was not a multiprotein form of polymerase alpha and the synchrony of the wheat germ embryos was not known. A possible tie between protein-synthesizing systems and the regulation of proteins involved in DNA replication may exist. The requirement of protein synthesis for the initiation of DNA replication has long been known. Also, it is well established that many temperature-sensitive mutants for tRNA synthetases are also DNA-synthesizing mutants. More investigation in this area may be warranted.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:5',5'''-P1, P4 diadenosine tetraphosphate (Ap4A): a putative initiator of DNA replication. 299 23

The purified high molecular weight form of HeLa cell DNA polymerase alpha (deoxynucleosidetriphosphate: DNA deoxynucleotidyltransferase, EC 2.7.7.7) was shown to associate tightly with several aminoacyl-tRNA synthetase activities. Fractionation of the high molecular weight enzyme on hexylagarose followed by gel filtration, chromatography on phosphocellulose, or polyacrylamide gel electrophoresis under nondenaturing conditions demonstrated copurification of only tryptophanyl-tRNA synthetase [L-tryptophan:tRNATrp ligase (AMP-forming), EC 6.1.1.2] along with DNA polymerase alpha. The high molecular weight (660,000) and low molecular weight (145,000) forms of DNA polymerase alpha were shown to possess a highly specific, noncovalent, diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) binding activity. The dissociation constants were determined to be 16 and 22 microM, respectively, by utilization of a charcoal adsorption procedure. No high-affinity binding of ATP could be detected. These findings suggest a link between the amino acid activation process and DNA replication in mammalian cells.
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PMID:HeLa cell DNA polymerase alpha is tightly associated with tryptophanyl-tRNA synthetase and diadenosine 5',5"'-P1,P4-tetraphosphate binding activities. 694 Jan 51

A combination of phylogenomic and signature sequence-based (or phenetic) approaches was used to understand the evolutionary relationships among cyanobacteria. Phylogenetic trees were constructed for 34 cyanobacteria whose genomes have been sequenced, based on concatenated sequences for 45 conserved proteins and also the 16S rRNA gene. In parallel, sequence alignments of various proteins were examined to identify conserved indels (i.e. molecular signatures or synapomorphies) that are specific for either all cyanobacteria or their various clades in the phylogenetic trees. Of the >40 molecular signatures described in this work, 15 are specific for all cyanobacteria. The other cyanobacterial clades that can now be identified and circumscribed in molecular terms by using these signatures include a deep-branching clade (clade A, corresponding to the subclass Gloeobacterophycidae), consisting of Gloeobacter violaceus and two diazotrophic Synechococcus strains (JA-3-3Ab and JA2-3-B'a) (15 aa insert in EF-G); a clade comprising all other cyanobacteria except those from clade A [18 aa insert in DNA polymerase I (Pol I), 2 aa insert in the DnaX protein, 4 aa insert in TrpRS and 4-5 aa insert in tryptophan synthase beta subunit]; a clade (clade C, corresponding to the subclass Synechococcophycidae) of various marine unicellular Synechococcus and Prochlorococcus cyanobacteria (12 aa insert in Pol I, 3 aa insert in RpoB, 2 aa insert in KgsA, 6 aa insert in TyrRS, 2 aa insert in tRNA-mG1 transferase and 1 aa deletion in the RpoC protein); a clade of the low-B/A ecotype Prochlorococcus strains (5 aa deletion in LeuRS and 1 aa insert in the Ffh protein); a clade consisting of the Nostocales species/strains (subclass Nostocophycidae; 4 aa insert in the PetA protein and 5 aa insert in the ribosomal protein S3); a clade of the order Chroococcales (1 aa insert in RecA); a clade comprising the orders Nostocales, Oscillatoriales and Chroococcales [19 aa insert in DnaE, 13 aa insert in GDP-mannose pyrophosphorylase and 22-27 aa insert in NADP(H)-quinone oxidoreductase subunit D]. Two additional conserved indels in the translation-initiation factor IF-2 and riboflavin synthase alpha subunit suggest an intermediate placement of the Oscillatoriales in between the orders Nostocales and Chroococcales. The unique presence of these molecular signatures in all available sequences from the indicated groups of cyanobacteria, but not in any other cyanobacteria (or bacteria), indicates that these synapomorphies provide novel and potentially useful means for circumscription of several important taxonomic clades of cyanobacteria in more definitive terms. The species-distribution patterns of these synapomorphies also indicate that the plant/plastid homologues are not derived from the clade A or C cyanobacteria.
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PMID:Protein signatures (molecular synapomorphies) that are distinctive characteristics of the major cyanobacterial clades. 1962 49