ABSTRACT
DNA containing short periodic stretches of adenine residues (known as A-tracts), which are aligned with the helical repeat, exhibit a pronounced macroscopic curvature. This property is thought to arise from the cumulative effects of a distinctive structure of the A-tract. It has also been observed by gel electrophoresis that macroscopic curvature is largely retained when inosine bases are introduced singly into A-tracts but decreases abruptly for pure I-tracts. The structural basis of this effect is unknown. Here we describe X-ray and gel electrophoretic analyses of several oligomers incorporating adenine or inosine bases or both. We find that macroscopic curvature is correlated with a distinctive base-stacking geometry characterized by propeller twisting of the base-pairs. Regions of alternating adenine and inosine bases display large propeller twisting comparable to that of pure A-tracts, whereas the values observed for pure I-tracts are significantly smaller. We also observe in the crystal structures that propeller twist leads to close cross-strand contacts between amino groups from adenine and cytosine bases, indicating an attractive NH-N interaction, which is analogous to the NH-O interaction proposed for A-tracts. This interaction also occurs between adenine bases across an A-T step and may explain in part the different behavior of A-T versus T-A steps in the context of A-tract-induced curvature. We also note that hydration patterns may contribute to propeller-twisted conformation. Based on the present data and other structural and biophysical studies, we propose that DNA macroscopic curvature is related to the structural invariance of A-tract and A-tract-like regions conferred by high propeller twist, cross-strand interactions and characteristic hydration. The implications of these findings to the mechanism of DNA bending are discussed.
Subject(s)
DNA/chemistry , Nucleic Acid Conformation , Adenine/chemistry , Crystallography, X-Ray , Electrophoresis, Polyacrylamide Gel , Inosine/chemistry , Models, Molecular , Molecular Sequence Data , Oligodeoxyribonucleotides/chemistry , Water/chemistryABSTRACT
Using data from Americans' Changing Lives: Wave 1, 1986, this study examined the long-term effects on the personal functioning of older women and men following the death of an adult child or a spouse. Guided by Weiss's (1993) theoretical framework, 41 bereaved parents and 143 bereaved spouses were compared to 407 nonbereaved adults on measures of perceived health, self-efficacy, depression, life satisfaction, and future orientation. Analyses revealed bereavement and gender effects and a consistent influence of the sociodemographic characteristics of education, income, and duration of bereavement on functioning.
Subject(s)
Adaptation, Psychological , Bereavement , Family , Life Change Events , Widowhood/psychology , Adult , Age Factors , Aged , Family/psychology , Female , Humans , Male , Quality of Life , Regression Analysis , Sampling Studies , Sex Factors , Time FactorsABSTRACT
Water molecules and DNA conformation are now recognized as ingredients which can influence both the affinity and specificity of protein/DNA complexes.
Subject(s)
DNA-Binding Proteins/chemistry , DNA , Nucleic Acid Conformation , Amino Acid Sequence , Base Sequence , Binding Sites , Conserved Sequence , Models, Molecular , Molecular Sequence Data , Thermodynamics , Water/chemistryABSTRACT
The hormone binding domain of the estrogen receptor is required not only for binding estradiol but also to form stable homodimers of the protein and mediate transcriptional activation by the receptor. Residues that are essential for estrogen binding are also involved in dimerization, suggesting that the hormone-binding pocket is at or near the dimer interface. Distinct hydrophobic and charged residues are essential for hormone-dependent transcriptional activation, and these appear to be conserved by other members of the nuclear receptor family. We have found that the pure antiestrogens ICI 164384 and ICI 182780 increase the turnover of the receptor compared with that in the presence of estradiol. Because it is likely that the pure antiestrogens bind to a similar region of the receptor as that of estradiol, we propose that they inhibit receptor dimerization by means of their 7 alpha alkyl-amide extension. It appears that as a consequence nuclear uptake is inhibited and the receptor more rapidly degraded in the cytoplasm.
Subject(s)
Receptors, Estrogen/metabolism , Animals , Estrogen Antagonists/pharmacology , Hormones/metabolism , Humans , Mutation , Receptors, Estrogen/drug effects , Receptors, Estrogen/genetics , Transcription, GeneticABSTRACT
We have investigated the effect of a series of steroidal oestrogen antagonists, related to ICI 164,384, on the DNA binding activity of mouse oestrogen receptors expressed in insect cells. The analogues possess different side chains at the 7-position of the B ring in the steroid. Inhibition was observed when the length of the side-chain was 15-16 carbon atoms but not 10 or 20 carbon atoms and only when the 7 alpha isomer was used. The DNA binding activity of receptors expressed in COS-1 cells was also inhibited after extended periods of incubation with antioestrogens but not that of the human receptor in breast cancer cell-extracts. We have proposed that ICI 164,384 might disrupt receptor dimerisation, and therefore the variation in its ability to inhibit DNA binding activity may reflect differences in dimer stability. Since the DNA binding activity of in vitro translated receptors was inhibited when they were translated in the presence of the antioestrogen we suggest that ICI 164,384 might prevent the formation of receptor dimers without necessarily being able to disrupt preformed dimers.
