摘要:

AbstractThe hexanucleotide Gm‐A‐A‐Y‐A‐ψp excised from the anticodon loop of yeast tRNAPheand its constituent oligonucleotides have been studied by ultraviolet absorption spectroscopy, static fluorescence, and circular dichroism. Gm‐Ap has a melting point of 45°C and a high melting enthalpy when compared with G‐Ap; hence 2′‐O‐methylation seems to stabilize stacking interactions. The nucleobase Y adjacent to the 3′‐side of the anticodon triplet interacts stronger with its 3′‐neighboring A than with its 5′‐neighboring A. It is concluded that the base Y disconnects the stack of the anticodon itself from the stack of the anticodon stem, thereby setting a reading frame for the mRNA in the course of protein biosynthesis. From the opposite signs of the short‐wavelength Cotton effects in the spectra of Gm‐A‐A‐Y‐Ap and Gm‐A‐A‐Y, it is concluded that Y after removal of its 3′ neighbor undergoes a dramatic change in its conformation. The fluorescence of the nucleobase Y upon addition of Mg2+is enhanced in oligonucleotides longer than two. An identical enhancement is observed for tRNAPhe, indicating that this Mg2+effect is a property of an oligonucleotide segment and does not reflect conformational changes of the whole tRNA. The data presented here reveal that the basic structural features of the anticodon loop are already present in the hexanucleotide Gm‐A‐A‐Y‐A

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140112

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe Miyazawa‐Blout‐Krimm (M‐B‐K) treatment of polypeptide absorption in the infrared is extended to the calculation of circular dichroism (CD), linear dichroism, and oriented CD for the amide I and amide II transitions. Matrix methods are applied to the α helix and β structures using measured values for the strengths and directions of the transition dipole moments and empirical values from M‐B‐K for the coupling constants.Relatively small aggregates, a 36‐residue helix, and 8‐chain × 4‐residue β sheets, are large enough to show calculated absorption agreeing with M‐B‐K results, which are based on infinite lattices.In all cases the predicted CD is an approximately conservative couple. The strongest CD should appear in the α helix, Δε/ε ≃± 10−3for both transitions. The amide II transition should show moderate CD couples in both β structures, Δε/ε ≃ (+2 to −1) × 10−4. The amide I transitions in β structures should show weak CD couples, Δε/ε = (+3 to −2) × 10−5, except that the negative branch in the antiparallel structure may be detectable (Δε/ε ≃ −2 × 10−4) because absorption is very low at its wavelength peak.CD on oriented samples should be enhanced over the unoriented cases, giving values as large as Δε/ε = 3 × 10−3because particular directions of observation allow the light to avoid much of the absorption in the sample.If all three structures are considered as helices, then the larger distance of the transition dipoles from the axis in the α helix, and the orientations of the transitions in the different structures, are the factors that, in terms of our previous theoretical work [Snir and Schellman (1973)J. Phys. Chem.77, 1653] satisfactorily explain the calculated results. Simple dipole–dipole interaction is cal

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140113

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe solution complexes of ethidium bromide with nine different deoxydinucleotides and the four self‐complementary ribodinucleoside monophosphates as well as mixtures of complementary and noncomplementary deoxydinucleotides were studied as models for the binding of the drug to DNA and RNA. Ethidium bromide forms the strongest complexes with pdC‐dG and CpG and shows a definite preference for interaction with pyrimidine–purine sequence isomers. Cooperativity is observed in the binding curves of the self‐complementary deoxydinucleotides pdC‐dG and pdG‐dC as well as the ribodinucleoside monophosphates CpG and GpC, indicating the formation of a minihelix around ethidium bromide. The role of complementarity of the nucleotide bases was evident in the visible and circular dichroism spectra of mixtures of complementary and noncomplementary dinucleotides. Nuclear magnetic resonance measurements on an ethidium bromide complex with CpG provided evidence for the intercalation model for the binding of ethidium bromide to double‐stranded nucleic acids. The results also suggest that ethidium bromide may bind to various sequences on DNA and RNA with significantly different bind

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140114

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractNative, NaCl‐treated, trypsin‐treated, and polylysine‐bound nucleohistones were studied in 2.5 × 10−4MEDTA, pH 8.0, using circular dichroism (CD) and thermal denaturation. Removal of histone I by 0.6MNaCl has a much smaller effect on both Δε220and Δε278than the removal of other histones. This indicates that histone I has less helical content and less conformational effect on the DNA in nucleohistone. By extrapolating to 100% binding by histones other than I, the positive CD band near 275 nm is close to zero. Comparison is also made between the effects of binding by the more basic and the less basic halves of histones by trypsin‐digestion and polylysine‐binding experiments. Trypsin digestion of nucleohistone reduces melting band IV at 82°C much more than melting band III at 72°C. However, the CD changes of Δε278and Δε220induced by trypsin digestion are small, unless melting band III is also reduced by the use of a higher trypsin level. This implies that the less basic halves of histones, which stabilize DNA to 72°C (melting band III), have more helical structure and are more responsible for conformational change in DNA than are the more basic halves, which stabilize DNA to 82°C (melting band IV). Polylysine binding to nucleohistone diminishes melting band III but has no effect on melting band IV. This binding affects only slightly the Δε220of nucleohistone, indicating that polylysine interferes very little with the structure of the less basic halves of bound histones. The implications of these studies with respect to chromat

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140115

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe structural features of calcium guanosine‐3′,5′‐cytidine monophosphate (GpC) have been elucidated by X‐ray diffraction analysis. The molecule was crystallized in space group P21with cell constants ofa= 21.224 Å,b= 34.207 Å,c= 9.327 Å, and β = 90.527°,Z= 8. The hydration of the crystal is 21% by weight with 72 water molecules in the unit cell. The four GpC molecules in the asymmetric unit occur as two Watson‐Crick hydrogen‐bonded dimers related by a pseudo‐C face centering. Each dimer consists of two independent GpC molecules whose bases are hydrogen bonded to each other in the traditional Watson‐Crick fashion. Each dimer possesses a pseudo twofold axis broken by a calcium ion and associated solvent.The four molecules are conformationally similar to helical RNA, but are not identical to it or to each other. Instead, values of conformational angles reflect the intrinsic flexibility of the molecule within the range of basic helical conformations. All eight bases areanti, sugars are all C3′‐endo, and the C4′‐C5′ bond rotations aregauche‐gauche.TheRfactor is 12.6% for 2918 observ

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140116

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140117

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140118

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1975.360140101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY