Heterochromatin protein 1 is involved in control of telomere elongation in Drosophila melanogaster

Telomeres of Drosophila melanogaster contain arrays of the retrotransposon-like elements HeT-A and TART. Their transposition to broken chromosome ends has been implicated in chromosome healing and telomere elongation. We have developed a genetic system which enables the determination of the frequency of telomere elongation events and their mechanism. The frequency differs among lines with different genotypes, suggesting that several genes are in control. Here we show that the Su(var)2-5 gene encoding heterochromatin protein 1 (HP1) is involved in regulation of telomere length. Different Su(var)2-5 mutations in the heterozygous state increase the frequency of HeT-A and TART attachment to the broken chromosome end by more than a hundred times. The attachment occurs through either HeT-A/TART transposition or recombination with other telomeres. Terminal DNA elongation by gene conversion is greatly enhanced by Su(var)2-5 mutations only if the template for DNA synthesis is on the same chromosome but not on the homologous chromosome. The Drosophila lines bearing the Su(var)2-5 mutations maintain extremely long telomeres consisting of HeT-A and TART for many generations. Thus, HP1 plays an important role in the control of telomere elongation in D. melanogaster.     

Critical effect of the N2 amino group on structure, dynamics, and elasticity of DNA polypurine tracts

Unrestrained 5-20-ns explicit-solvent molecular dynamics simulations using the Cornell et al. force field have been carried out for d[GCG(N)11GCG]2 (N, purine base) considering guanine*cytosine (G*C), adenine*thymine (A*T), inosine*5-methyl-cytosine (I*mC), and 2-amino-adenine*thymine (D*T) basepairs. The simulations unambiguously show that the structure and elasticity of N-tracts is primarily determined by the presence of the amino group in the minor groove. Simulated A-, I-, and AI-tracts show almost identical structures, with high propeller twist and minor groove narrowing. G- and D-tracts have small propeller twisting and are partly shifted toward the A-form. The elastic properties also differ between the two groups. The sequence-dependent electrostatic component of base stacking seems to play a minor role. Our conclusions are entirely consistent with available experimental data. Nevertheless, the propeller twist and helical twist in the simulated A-tract appear to be underestimated compared to crystallographic studies. To obtain further insight into the possible force field deficiencies, additional multiple simulations have been made for d(A)10, systematically comparing four major force fields currently used in DNA simulations and utilizing B and A-DNA forms as the starting structure. This comparison shows that the conclusions of the present work are not influenced by the force field choice.     

Structural features of two distinct molecular complexes of copper(II) cationic porphyrin and deoxyribonucleotides

The associations of the water-soluble cationic copper(II)-5,10,15,20-meso-tetrakis(4-N-methylpyridyl) porphyrin (CuP) with d(pT)9 oligothymidylate and its building blocks deoxythymidine (dT) and deoxythymidine 5'-monophosphate (dTMP) were investigated by spectrophotometric titration [absorption, nanosecond transient resonance Raman (ns-RR) and picosecond time-resolved resonance Raman (ps-TR3) spectroscopies] to elucidate the structural requirements for the CuP exciplex formation in molecular complexes with unchained mononucleotides. In the d(pT)9 a factor analysis and global fit of the CuP absorption spectra revealed the formation of a single spectral species attributable to a 1 : 1 CuP. d(pT)9 complex throughout a wide range of d(pT)9/CuP ratios (0-10). Using ps-TR3 spectroscopy, the CuP. d(pT)9 complex was shown to be fully responsible for exciplex formation. In contrast, CuP mixed with dTMP ([dTMP]/[CuP] < 3000) yielded two spectroscopically distinct types of molecular complexes with 1 : 1 (CuP. dTMP) and 1 : 2 (CuP. (dTMP)2) (or even higher for [dTMP]/[CuP] > 3000) stoichiometry, the latter being spectroscopically identical to the CuP. d(pT)9 and providing a microenvironment favorable for exciplex formation to the same extent as the oligothymidylate. On the other hand, the 1 : 1 CuP. dTMP complex (prevailing for [dTMP]/[CuP] < 100) yielded no exciplex features. Similar behavior was observed for the CuP complexed with dT. To explain the difference in the ability of the CuP. dTMP and CuP. (dTMP)2 species to form the exciplex, two types of molecular complexes were suggested and discussed, differing in the orientation of the thymine planes with respect to the porphyrin macrocycle.     

Computer literacy enhancement in the Teaching Hospital Olomouc. Part I: project management techniques. Short communication

Information explosion and globalization make great demands on keeping pace with the new trends in the healthcare sector. The contemporary level of computer and information literacy among most health care professionals in the Teaching Hospital Olomouc (Czech Republic) is not satisfactory for efficient exploitation of modern information technology in diagnostics, therapy and nursing. The present contribution describes the application of two basic problem solving techniques (brainstorming, SWOT analysis) to develop a project aimed at information literacy enhancement.     

Experimental modelling of thermal inactivation of urease

Thermal inactivation of jack bean urease (EC 3.5.1.5) was investigated in a 0.1 M phosphate buffer with pH 7. An injection flow calorimetry method was adapted for the measurement of the enzyme activity. The inactivation curves were measured in the temperature range of 55 to 87.5 degrees C. The curves exhibited a biphasic pattern in the whole temperature range and they were well fitted with a biexponential model. A simultaneous fit of all inactivation data was based on kinetic models that were derived from different inactivation mechanisms and comprised the material balances of several enzyme forms and the enthalpy balance characterizing the initial heating period of enzyme solution. The multitemperature evaluation revealed that an adequate model had to incorporate at least three reaction steps. It was concluded that the key reaction steps at urease thermal inactivation were the reversible dissociation/denaturation of native form into an inactive denatured form, and irreversible association reactions of both the denatured and native forms.     

Recoverin is a zinc-binding protein

Recoverin is an N-myristoylated 23 kDa calcium-binding protein from retina, which modulates the Ca2+-sensitive deactivation of rhodopsin via Ca2+-dependent inhibition of rhodopsin kinase. It was shown by intrinsic and bis-ANS probe fluorescence, circular dichroism, and differential scanning calorimetry that myristoylated recombinant recoverin interacts specifically with zinc ions. Similar to the calcium binding, the binding of zinc to Ca2+-loaded recoverin additionally increases its alpha-helical content, hydrophobic surface area, and environmental mobility/polarity of its tryptophan residues. In contrast to the calcium binding, the binding of zinc decreases thermal stability of the Ca2+-loaded protein. Zn2+-titration of recoverin, traced by bis-ANS fluorescence, reveals binding of a single Zn2+ ion per protein molecule. It was shown that the double-mutant E85Q/E121Q with inactivated Ca2+-binding EF-hands 2 and 3 (Alekseev, A. M.; Shulga-Morskoy, S. V.; Zinchenko, D. V.; Shulga-Morskaya, S. A.; Suchkov, D. V.; Vaganova, S. A.; Senin, I. I.; Zargarov, A. A.; Lipkin, V. M.; Akhtar, M.; Philippov, P. P. FEBS Lett. 1998, 440, 116-118), which can be considered as an analogue of the apo-protein, binds Zn2+ ion as well. Apparent zinc equilibrium binding constants evaluated from spectrofluorimetric Zn2+-titrations of the protein are 1.4 x 10(5) M(-1) (dissociation constant 7.1 microM) for Ca2+-loaded wild-type recoverin and 3.3 x 10(4) M(-1) (dissociation constant 30 microM) for the E85Q/E121Q mutant (analogue of apo-recoverin). Study of the binding of wild-type recoverin to ROS membranes showed a zinc-dependent increase of its affinity for the membranes, without regard to calcium content, suggesting further solvation of a protein myristoyl group upon Zn2+ binding. Possible implications of these findings to the functioning of recoverin are discussed.     

Site-specific cleavage of RNA and DNA by complementary DNA--bleomycin A5 conjugates

Bleomycin displays clinical chemotherapeutic activity, but is so nonspecifically toxic that it is rarely administered. It was therefore of interest to determine whether bleomycin could be directed to cleave RNA or DNA at a specific site by conjugation to a complementary oligonucleotide. A 15 nt MYC complementary oligodeoxynucleotide (HMYC55) bearing a 5' bleomycin A5 (Blm) residue was designed to base-pair with nt 7047-7061 of human MYC mRNA. Reactivity of the Blm-HMYC55 conjugate (and mismatch controls) with a MYC mRNA 30-mer, a MYC DNA 30-mer, and a MYC 2'-O-methyl RNA 30-mer, nt 7041-7070, was analyzed in 100 microM FeNH(4)SO(4), 50 mM beta-mercaptoethanol, 200 mM LiCl, 10 mM Tris-HCl, pH 7.5, at 37 degrees C. Cleavage of the substrate RNA or DNA occurred primarily at the junction of the complementary DNA-target RNA duplex, 18-22 nt from the 5' end of the RNA. Reaction products with lower mobility than the target RNA or DNA also formed. Little or no reaction was observed with more than three mismatches in a Blm-oligodeoxynucleotide conjugate. Neither the short RNA or DNA cleavage fragments nor the low mobility products were observed in the absence of Fe(II), or the presence of excess EDTA. The target RNA was also cleaved efficiently by bleomycin within a hybrid duplex with a preformed single-nucleotide bulge in the RNA strand. New Blm-oligodeoxynucleotide conjugates containing long hexaethylene glycol phosphate based linkers between oligodeoxynucleotide and bleomycin were designed to target this bulge region. These conjugates achieved 8-18% cleavage of the target RNA, depending on the length of the linker. Blm-oligodeoxynucleotide conjugates thus demonstrated sequence specificity and site specificity against RNA and DNA targets.     

Crystal structure of <Emphasis Type="Italic">Escherichia coli</Emphasis> protein ybgI,a toroidal structure with a dinuclear metal site

Background

The protein encoded by the gene ybgI was chosen as a target for a structural genomics project emphasizing the relation of protein structure to function.

Results

The structure of the ybgI protein is a toroid composed of six polypeptide chains forming a trimer of dimers. Each polypeptide chain binds two metal ions on the inside of the toroid.

Conclusion

The toroidal structure is comparable to that of some proteins that are involved in DNA metabolism. The di-nuclear metal site could imply that the specific function of this protein is as a hydrolase-oxidase enzyme.