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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The transport of thymidine by the protozoan parasite Giardia intestinalis was examined at 0 degrees C. This temperature prevented attachment of the cells to vessel walls, so that a rapid sampling technique could be used. Thymidine influx (distinguished from gross uptake) was readily measurable at 0 degrees C and was specific and saturable. The transporter appears to be a facilitative carrier, exhibiting a high affinity for thymidine (Km = 50 microM). Thymine and uracil were the most effective inhibitors (Ki = 30 microM and 45 microM, respectively), followed by thymidine, deoxyuridine and uridine (Ki = 64-96 microM). Cytosine, cytidine and deoxycytidine were not inhibitory, even at high concentrations. The data indicate that the oxygen at position 4 of the pyrimidine ring is essential for recognition by the transporter, whereas the 5-methyl group of thymine is unimportant. The furanose ring appears not to be recognized, since D-ribose was non-inhibitory and uridine and deoxyuridine were equally inhibitory but less so than uracil and thymine. This carrier probably mediates the transport of uracil, as well as uridine and thymidine, although influx of the base remains to be measured.
Mol Biochem Parasitol 1991 Oct
PMID:Characteristics of thymidine transport in Giardia intestinalis trophozoites. 176 28

The coding repeat region of opa genes from Neisseria gonorrhoeae and Neisseria meningitidis determines the expression state of their respective genes through high-frequency addition of deletion of pentanucleotide coding repeat units (CRs; CTTCT). In vitro analyses of cloned opa gene CR regions using single-strand specific nucleases, oligonucleotide protection experiments, and modifications of non-B-DNA residues indicate that the regions form structures resembling H-DNA under acidic conditions in the presence of negative supercoiling. The purine/pyrimidine strand bias and H-palindromic nature of the repeat region are consistent with sequence requirements for H-DNA formation. Sequences flanking the repeat elements are required to form the H-DNA structure in vitro as judged by the pattern of exposed non-B-DNA residues in CR sequences synthesized as oligonucleotides to form beta-galactosidase::CR translational fusions. The fusions phase vary by addition and deletion of CR elements and the rate of phase variation increases upon induction of the fusion genes. The opa gene CR region is the first reported bacterial H-DNA structure and is unique in that it lies within the coding sequence for the gene.
Mol Microbiol 1991 Oct
PMID:H-DNA formation by the coding repeat elements of neisserial opa genes. 179 51

In this study, we analyzed 10 human squamous cell carcinomas (SCCs) for alterations in the p53 tumor suppressor gene in exons 4 through 9 by single-strand conformation polymorphism (SSCP) analysis. We found that 2 of 10 SCCs displayed unusual SSCP alleles at exon 7 of the p53 gene. Subsequent cloning and sequencing of PCR-amplified exon 7 DNA from these two tumors revealed that one had a G----A transition at the first position of codon 244, predicting a glycine-to-serine amino acid change, while the other tumor exhibited a G----T base change at the second nucleotide of codon 248, predicting an arginine-to-leucine substitution. Because the mutations in the p53 tumor suppressor gene in both tumors were located opposite potential pyrimidine dimer sites (C-C), it is consistent with these mutations having been induced by the ultraviolet radiation present in sunlight. These studies demonstrate that inactivation of the p53 tumor suppressor gene, as well as activation of ras oncogenes, may be involved in the pathogenesis of some human skin cancers.
Mol Carcinog 1991
PMID:Mutations in the p53 tumor suppressor gene in human cutaneous squamous cell carcinomas. 179 82

Relationship between pyrimidine distribution patterns and radiosensitivity (Z) of DNA molecules of different species was derived by computer analysis of recurrence frequency of pyrimidine clusters. Blocking factors (beta) and Z for coding and non-coding DNA sequences of species from different taxonomic classes have been calculated within a new model. The radiosensitivity of coding DNA sequences practically does not vary whereas Z values were increased during evolution from simplest to higher organisms. The beta and Z values calculated for several groups of individual genes were shown to vary considerably.
Mol Biol (Mosk)
PMID:[Radiosensitivity of coding and noncoding DNA sequences of various organisms]. 181 7

The mitochondrial DNA of trypanosomes is composed of maxicircle and minicircle DNAs catenated into a network, called the kinetoplast. Maxicircles encode proteins and RNAs necessary for mitochondrial assembly. Minicircles encode small transcripts which are believed to serve as guide RNAs in the process of RNA editing of maxicircle transcripts. Trypanosoma equiperdum minicircles contain three transcription units which produce three distinct transcripts. The genes for these transcripts are flanked by imperfect 18-bp repeats separated by approximately 110 bp. The transcripts have a 5' triphosphate, indicating that they are primary transcripts. Minicircle transcription initiates at a purine within a conserved sequence, 5'-AYAYA-3', where Y is a pyrimidine, 32 bp from the upstream inverted repeat, suggesting that the repeats may function in transcript initiation. Transcripts from a single minicircle transcription unit range in size from 55 to 70 nucleotides. This size heterogeneity within a single sequence class is due to the variable length of nontemplated uridine residues composing a 3' tail. The size range and heterogeneous polyuridylate 3' end of the minicircle transcripts appear to be conserved features and may be related to transcript function.
Mol Cell Biol 1991 Mar
PMID:Trypanosoma equiperdum minicircles encode three distinct primary transcripts which exhibit guide RNA characteristics. 182 48

The sequencing and comparison of the genes encoding the glyoxylate bypass enzyme malate synthase of Aspergillus nidulans (acuE) and Neurospora crassa (acu-9) are presented. The predicted amino acid sequences of the A. nidulans and N. crassa enzymes are 538 and 542 residues respectively and the proteins are 87% homologous. In fungi, the malate synthase proteins are located in glyoxysomes and the deduced acuE and acu-9 proteins both contain a C-terminal S-K-L sequence, which has been implicated in transport into peroxisomes. The acuE coding region is interrupted by four introns and the acu-9 coding region is interrupted by one intron which occurs at the same position as the C-terminal acuE intron. The 5' non-coding regions of the two genes were examined for short homologous sequences that may represent the binding sites for regulatory proteins. Pyrimidine-rich sequences with weak homology to the amdI9 sequence, which has been implicated in facB-mediated acetate regulation of the amdS gene, were found but their functional significance remains to be determined.
Mol Gen Genet 1991 Sep
PMID:Molecular organisation of the malate synthase genes of Aspergillus nidulans and Neurospora crassa. 183 36

A cDNA containing the entire coding region for the iron storage protein ferritin has been isolated from the French bean plant, Phaseolus vulgaris L. cv. Tendergreen. Ferritin protein was purified from young leaves and shoot meristem tissue and used to raise antisera in mice. A lambda gt11 cDNA library was constructed from seed-derived poly(A)+ RNA, and screened with the mouse anti-ferritin serum. A 1.2 kb immunopositive phage DNA insert was isolated and sequenced. The derived amino acid sequence shows substantial similarity with other ferritin sequences. The 5' untranslated region contains two out-of-frame AUG codons, a region of extreme pyrimidine composition bias and potentially stable secondary structure.
Plant Mol Biol 1991 Sep
PMID:The structure of a Phaseolus vulgaris cDNA encoding the iron storage protein ferritin. 188

One variant, aphhs-3 was previously isolated based on a hypersensitivity to nontoxic concentrations of aphidicolin, a specific inhibitor of DNA polymerases-alpha and delta. This variant was found to be more sensitive to temperatures above 35 degrees C and to 10 microM of 3'-azido-3'-deoxythymidine (zidovudine, azidothymidine, or AZT) than the parental 743x cells. DNA polymerase activities in the cell extract or in the partially purified fraction by DEAE-cellulose (DE52) anion exchange column from aphhs-3 were active at 40 degrees C. No significant differences in deoxynucleoside triphosphate pools were observed at 34 degrees C for both the parental 743x and aphhs-3 cells. Revertants were isolated at 39 degrees C: six revertants (aphhs-3-tr1 through aphhs-3-tr6) were obtained without aphidicolin; one revertant aphhs-3-tar (the tar clone) was selected in aphidicolin (0.12 microM). The hypersensitivity to aphidicolin (Aphhs) and AZT (AZThs) was cosegregated in the revertant aphhs-3-tr5 (the tr5 clone), while the tar clone was not AZThs. There was a similar increase in the specific activity of 3H-labeled DNA in all cell lines after additions of [3H]AZT or [3H]thymidine. Additions of purine or pyrimidine arabinosides (araT, araC, and araA) to all cell lines resulted in a similar cytotoxicity, suggesting the anabolism of dTTP was not defective in the tr5 clone. The spontaneous mutation rate at the hypoxanthine-guanine phosphoryltransferase locus using replating techniques and 6-thioguanine resistance selection was less than or equal to 5 x 10(-7), 2.2 x 10(-6), or 1.3 x 10(-6) per generation for the tr5, 743x, or tar cell lines, respectively. Most importantly, DNA polymerase activities in the cell extract of the revertant tr5 clone were inhibited by 0.5 microM AZTTP. In contrast, no inhibition was observed in those of the parental 743x and revertant tar cells. The cosegregation of both Aphhs and AZThs in the tr5 revertant suggests that these two phenotypes may be a result of the same mutational event.
Somat Cell Mol Genet 1991 Jan
PMID:Mutants from V79 fibroblasts exhibiting hypersensitivity to aphidicolin and 3'-azido-3'-deoxythymidine. 190 Jan 32

Recently, P.A. Beal and P.B. Dervan, expanding on earlier observations by others, have established the formation of purine.purine.pyrimidine triple helices stabilized by G.GC, A.AT and T.AT base triples where the purine-rich third strand was positioned in the major groove of the Watson-Crick duplex and anti-parallel to its purine strand. The present nuclear magnetic resonance (n.m.r.) study characterizes the base triple pairing alignments and strand direction in a 31-mer deoxyoligonucleotide that intramolecularly folds to generate a 7-mer (R/Y-)n.(R+)n(Y-)n triplex with the strands linked by two T5 loops and stabilized by potential T.AT and G.GC base triples. (R and Y stand for purine and pyrimidine, respectively, while the signs establish the strand direction.) This intramolecular triplex gives well-resolved exchangeable and non-exchangeable proton spectra with Li+ as counterion in aqueous solution. These studies establish that the T1 to C7 pyrimidine and the G8 to A14 purine strands are anti-parallel to each other and align through Watson-Crick A.T and G.C pair formation. The T15 to G21 purine-rich third strand is positioned in the major groove of this duplex and pairs through Hoogsteen alignment with the purine strand to generate T.AT and G.GC triples. Several lines of evidence establish that the thymidine and guanosine bases in the T15 to G21 purine-rich third strand adopt anti glycosidic torsion angles under conditions where this strand is aligned anti-parallel to the G8 to A14 purine strand. We have also recorded imino proton n.m.r. spectra for an (R-)n.(R+)n(Y-)n triplex stabilized by G.GC and A.AT triples through intramolecular folding of a related 31-mer deoxyoligonucleotide with Li+ as counterion. The intramolecular purine.purine.pyrimidine triplexes containing unprotonated G.GC, A.AT and T.AT triples are stable at basic pH in contrast to pyrimidine.purine.pyrimidine triplexes containing protonated C+.GC and T.AT triples, which are only stable at acidic pH.
J Mol Biol 1991 Oct 20
PMID:Nuclear magnetic resonance structural studies of intramolecular purine.purine.pyrimidine DNA triplexes in solution. Base triple pairing alignments and strand direction. 194 59

Glutamine-dependent carbamoyl-phosphate synthetase (EC 6.3.5.5) catalyzes the first step in de novo pyrimidine biosynthesis. The mammalian enzyme is part of a 240-kDa multifunctional protein which also has the second (aspartate carbamoyltransferase, EC 2.1.3.2), and third (dihydroorotase, EC 3.5.2.3) activities of the pathway. Shigesada et al. (Shigesada, K., Stark, G.R., Maley, J.A., and Davidson, J.N. (1985) Mol. Cell Biol. 175, 1-7) produced a truncated cDNA clone from a Syrian hamster cell line that contained most of the coding region for this protein. We have completed sequencing this clone, known as pCAD142. The cDNA insert contained all of the coding region for the glutaminase (GLN) and carbamyl phosphate synthetase (CPS) domains but lacked a short amino-terminal segment. By comparing the primary structure of the mammalian chimera to monofunctional proteins we have identified the borders of the functional domains. The GLN domain is 21 kDa, close to the size of the functionally similar polypeptide products of the Escherichia coli pabA and hisH genes. The domain has the three regions of homology common to trpG-type glutamine amidotransferases, as well as a fourth region specific to the carbamyl phosphate synthetases. The CPSase domain is similar to other reported CPSases in size (120 kDa), primary structure (37-67% amino acid identity), and homology between its amino and carboxyl halves. Analysis of the nucleotide and amino acid sequence identities among the various carbamyl phosphate synthetases suggests that the gene fusion which joined the GLN and CPS domains was an early event in the evolution of eukaryotic organisms and that the Saccharomyces cerevisiae enzyme consisting of separate subunits arose by defusion from an ancestral multifunctional protein.
 ...
PMID:Mammalian carbamyl phosphate synthetase (CPS). DNA sequence and evolution of the CPS domain of the Syrian hamster multifunctional protein CAD. 197 79


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