Luisa Franco - Academia.edu (original) (raw)
Papers by Luisa Franco
Biochemistry, 1994
Multiple enzyme forms of histone deacetylase and histone acetyltransferase exist in germinating m... more Multiple enzyme forms of histone deacetylase and histone acetyltransferase exist in germinating maize embryos. We analyzed the association of the different enzymes to chromatin by ion exchange chromatography of subcellular fractions from different time points of embryo germination. The vast majority of histone deacetylase HD-1A was not bound to chromatin, since it was solubilized during chromatin isolation, regardless of its phosphorylation state and the phase of embryo germination. In contrast, HD-2 was chromatin bound during the entire germination pathway. Histone deacetylase HD-1B was present in a chromatin-bound and a soluble form; the ratio between these two forms changed during germination. Both nuclear histone acetyltransferases, HAT-A1 and HAT-A2, were tightly chromatin-bound and could only be released from chromatin by salt extraction. To test whether histone acetyltransferases or deacetylases are associated with the nuclear matrix, we analyzed nuclear matrix preparations from yeast, Physarum, and maize step by step for both enzyme activities. This analysis confirmed that part of the activity is chromatin bound, but no significant enzyme activity could be found in the final nuclear matrix, regardless of the preparation protocol. This result was further substantiated by detailed analysis of histone deacetylases and acetyltransferases during cellular fractionation and nuclear matrix preparation of chicken erythrocytes. Altogether our results suggest that the participation of these enzymes in different nuclear processes may partly be regulated by a distinct location to intranuclear components.
Febs Letters, 1993
Core histones can be modified by reversible, posttranslational acetylation of specific lysine res... more Core histones can be modified by reversible, posttranslational acetylation of specific lysine residues within the N-terminal protein domains. The dynamic equilibrium of acetylation is maintained by two enzyme activities, histone acetyltransferase and histone deacetylase. Recent data on histone deacetylases and on anionic motifs in chromatin-or DNA-binding regulatory proteins (e.g. transcription factors, nuclear proto-oncogenes) are summarized and united into a hypothesis which attributes a key function to histone deacetylation for the binding of regulatory proteins to chromatin by a transient, specific local increase of the positive charge in the N-terminal domains of nucleosomal core histones. According to our model, the rapid deacetylation of distinct lysines in especially H2A and H2B would facilitate the association of anionic protein domains of regulatory proteins to specific nucleosomes. Therefore histone deacetylation (histone deacetylases) may represent a unique regulatory mechanism in the early steps of gene activation, in contrast to the more structural role of histone acetylation (histone acetyltransferases) for nucleosomal transitions during the actual transcription process.
Macromolecules, 1996
Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and... more Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and 8 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy; both imaging and diffraction. Sedimented mats were examined using X-ray diffraction. The solution grown single crystals are lath-shaped lamellae. Diffraction from these crystals, at room temperature, reveals that three crystalline forms are commonly present. The crystals are composed of chain-folded, hydrogen-bonded sheets; the linear hydrogen bonds within the sheets generate a progressive shear of the chains. The sheets are found to stack in two different ways; some of the sheets stack with progressive shear, to form 'c~-phase' crystals; other sheets stack with alternate up and down stagger, to form ";7-phase' crystals. Both the c~-and ~3-crystals give two strong diffraction signals at spacings of 0.44 and 0.37 nm; these signals represent a projected inter-chain distance within a hydrogen-bonded sheet (actual value 0.48 nm) and the inter-sheet spacing, respectively. Some crystals also show an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudo-hexagonal phase, a phase usually only found at high temperatures. The melting points of solution grown crystals of this even-even nylon series decrease with decreasing linear density of hydrogen bonds. On heating, the strong diffraction signals in both c~-and/3-phases move together and meet, as is the case for other even-even nylons. The lowest temperature at which the two signals first have the same spacing is termed the Brill temperature. For all the nylons of the present study the Brill temperature is coincident with the melting temperature, and the two strong signals meet at the spacing (0.42 nm) of the pseudo-hexagonal phase. The behaviour of these nylons is compared and contrasted with that of nylon 6 6, where only the c~-phase is found at room temperature and, on heating, the Brill temperature is found to occur in the range 95-35°C below the melting point at 265°C. ~, 1997 Elsevier Science Ltd.
Macromolecules, 1997
ABSTRACT Nylons 8 10 and 10 12 have been synthesized and crystallized as chain-folded lamellae fr... more ABSTRACT Nylons 8 10 and 10 12 have been synthesized and crystallized as chain-folded lamellae from 1,4-butanediol and the results compared with previous studies on Nylons 4 6 and 6 8. In 2N 2(N + 1) Nylons, the lengths of the two alkane segments are equal and two different hydrogen-bonded sheet schemes are possible: progressive or alternating shear. At room temperature, Nylons 8 10 and 10 12 adopt the progressive scheme and the adjacent re-entry folds in the crystals must be in the alkane chain segments. In contrast, Nylons 4 6 and 6 8 lamellae, crystallized from the same solvent, exhibit the alternating hydrogen bonding scheme and each adjacent re-entry fold must contain an amide group. The transition in the chemical nature of the lamellar surface, from the amide fold to the alkane fold, occurs in passing from Nylon 6 8 to 8 10. Thus, the progressive hydrogen-bonded sheet/alkane fold structure is energetically more favorable, provided the alkane-folding geometry is sufficiently relaxed; this comes with increasing alkane segment length. For each hydrogen-bonded sheet structure there are still two principal intersheet stacking modes in lamellar crystals: the progressively sheared α-phase or the alternatingly sheared β-phase, both of which have been found in the 8 10 and 10 12 Nylons. The 2N 2(N + 1) Nylons have the choice of four possible structures. The melting points of solution grown crystals of Nylons 4 6, 6 8, 8 10, and 10 12 decrease with decreasing intrachain amide density. When lamellar crystals of these Nylons are heated, the two characteristic interchain diffraction signals move together and meet at their Brill temperature; for Nylon 10 12 it appears to be close to the melting point.
Journal of Polymer Science Part B-polymer Physics, 1997
Four members of the even-even nylon 2 Y series, for Y Å 6, 8, 10, and 12, have been crystallized ... more Four members of the even-even nylon 2 Y series, for Y Å 6, 8, 10, and 12, have been crystallized in the form of chain-folded lamellar single crystals from 1,4butanediol and studied by transmission electron microscopy ( imaging and diffraction ) , x-ray diffraction, and thermal analysis. The structures of these 2 Y nylons are different from those of nylon 6 6 and many other even-even nylons. At room temperature, two strong diffraction signals are observed at spacings 0.42 and 0.39 nm, respectively; these values differ from the 0.44 and 0.37 nm diffraction signals observed for nylon 6 6 and most even-even nylons at ambient temperature. Detailed analyses of the diffraction patterns show that all these 2 Y nylons have triclinic unit cells. The diamine alkane segments of 2 Y nylons are too short to sustain chain folds; thus, the chain folds must be in the diacid alkane segments in all cases. On heating the crystals from room temperature to the melt, the triclinic structures transform into pseudohexagonal structures and the two diffraction signals meet at the Brill transition temperature which occurs significantly below the melting point. The room temperature structures of these 2 Y nylons are similar to the unit cell of nylon 6 6 at elevated temperature, but below its Brill temperature. The room temperature structures and behavior on heating of the nylon 2 Y family is noticeably different from that of the even-even nylon X 4 family, although the only difference between these families of polyamides is the relative disposition of the amide groups within the chains. The results show that in order to understand the structure, behavior and properties of crystalline nylons, especially as a function of temperature, the detailed stereochemistry needs to be taken into account.
Polymer, 1997
Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and... more Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and 8 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy; both imaging and diffraction. Sedimented mats were examined using X-ray diffraction. The solution grown single crystals are lath-shaped lamellae. Diffraction from these crystals, at room temperature, reveals that three crystalline forms are commonly present. The crystals are composed of chain-folded, hydrogen-bonded sheets; the linear hydrogen bonds within the sheets generate a progressive shear of the chains. The sheets are found to stack in two different ways; some of the sheets stack with progressive shear, to form 'c~-phase' crystals; other sheets stack with alternate up and down stagger, to form ";7-phase' crystals. Both the c~-and ~3-crystals give two strong diffraction signals at spacings of 0.44 and 0.37 nm; these signals represent a projected inter-chain distance within a hydrogen-bonded sheet (actual value 0.48 nm) and the inter-sheet spacing, respectively. Some crystals also show an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudo-hexagonal phase, a phase usually only found at high temperatures. The melting points of solution grown crystals of this even-even nylon series decrease with decreasing linear density of hydrogen bonds. On heating, the strong diffraction signals in both c~-and/3-phases move together and meet, as is the case for other even-even nylons. The lowest temperature at which the two signals first have the same spacing is termed the Brill temperature. For all the nylons of the present study the Brill temperature is coincident with the melting temperature, and the two strong signals meet at the spacing (0.42 nm) of the pseudo-hexagonal phase. The behaviour of these nylons is compared and contrasted with that of nylon 6 6, where only the c~-phase is found at room temperature and, on heating, the Brill temperature is found to occur in the range 95-35°C below the melting point at 265°C. ~, 1997 Elsevier Science Ltd.
Estamos en un momento crítico de la historia de la Tierra, en el cual la humanidad debe elegir su... more Estamos en un momento crítico de la historia de la Tierra, en el cual la humanidad debe elegir su futuro. A medida que el mundo se vuelve cada vez más interdependiente y frágil, el futuro depara, a la vez, grandes riesgos y grandes promesas. Para seguir adelante, debemos reconocer que en medio de la magnífica diversidad de culturas y formas de vida, somos una sola familia humana y una sola comunidad terrestre con un destino común. Debemos unirnos para crear una sociedad global sostenible fundada en el respeto hacia la naturaleza, los derechos humanos universales, la justicia económica y una cultura de paz. En torno a este fin, es imperativo que nosotros, los pueblos de la Tierra, declaremos nuestra responsabilidad unos hacia otros, hacia la gran comunidad de la vida y hacia las generaciones futuras.
Biochemistry, 1994
Multiple enzyme forms of histone deacetylase and histone acetyltransferase exist in germinating m... more Multiple enzyme forms of histone deacetylase and histone acetyltransferase exist in germinating maize embryos. We analyzed the association of the different enzymes to chromatin by ion exchange chromatography of subcellular fractions from different time points of embryo germination. The vast majority of histone deacetylase HD-1A was not bound to chromatin, since it was solubilized during chromatin isolation, regardless of its phosphorylation state and the phase of embryo germination. In contrast, HD-2 was chromatin bound during the entire germination pathway. Histone deacetylase HD-1B was present in a chromatin-bound and a soluble form; the ratio between these two forms changed during germination. Both nuclear histone acetyltransferases, HAT-A1 and HAT-A2, were tightly chromatin-bound and could only be released from chromatin by salt extraction. To test whether histone acetyltransferases or deacetylases are associated with the nuclear matrix, we analyzed nuclear matrix preparations from yeast, Physarum, and maize step by step for both enzyme activities. This analysis confirmed that part of the activity is chromatin bound, but no significant enzyme activity could be found in the final nuclear matrix, regardless of the preparation protocol. This result was further substantiated by detailed analysis of histone deacetylases and acetyltransferases during cellular fractionation and nuclear matrix preparation of chicken erythrocytes. Altogether our results suggest that the participation of these enzymes in different nuclear processes may partly be regulated by a distinct location to intranuclear components.
Febs Letters, 1993
Core histones can be modified by reversible, posttranslational acetylation of specific lysine res... more Core histones can be modified by reversible, posttranslational acetylation of specific lysine residues within the N-terminal protein domains. The dynamic equilibrium of acetylation is maintained by two enzyme activities, histone acetyltransferase and histone deacetylase. Recent data on histone deacetylases and on anionic motifs in chromatin-or DNA-binding regulatory proteins (e.g. transcription factors, nuclear proto-oncogenes) are summarized and united into a hypothesis which attributes a key function to histone deacetylation for the binding of regulatory proteins to chromatin by a transient, specific local increase of the positive charge in the N-terminal domains of nucleosomal core histones. According to our model, the rapid deacetylation of distinct lysines in especially H2A and H2B would facilitate the association of anionic protein domains of regulatory proteins to specific nucleosomes. Therefore histone deacetylation (histone deacetylases) may represent a unique regulatory mechanism in the early steps of gene activation, in contrast to the more structural role of histone acetylation (histone acetyltransferases) for nucleosomal transitions during the actual transcription process.
Macromolecules, 1996
Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and... more Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and 8 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy; both imaging and diffraction. Sedimented mats were examined using X-ray diffraction. The solution grown single crystals are lath-shaped lamellae. Diffraction from these crystals, at room temperature, reveals that three crystalline forms are commonly present. The crystals are composed of chain-folded, hydrogen-bonded sheets; the linear hydrogen bonds within the sheets generate a progressive shear of the chains. The sheets are found to stack in two different ways; some of the sheets stack with progressive shear, to form 'c~-phase' crystals; other sheets stack with alternate up and down stagger, to form ";7-phase' crystals. Both the c~-and ~3-crystals give two strong diffraction signals at spacings of 0.44 and 0.37 nm; these signals represent a projected inter-chain distance within a hydrogen-bonded sheet (actual value 0.48 nm) and the inter-sheet spacing, respectively. Some crystals also show an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudo-hexagonal phase, a phase usually only found at high temperatures. The melting points of solution grown crystals of this even-even nylon series decrease with decreasing linear density of hydrogen bonds. On heating, the strong diffraction signals in both c~-and/3-phases move together and meet, as is the case for other even-even nylons. The lowest temperature at which the two signals first have the same spacing is termed the Brill temperature. For all the nylons of the present study the Brill temperature is coincident with the melting temperature, and the two strong signals meet at the spacing (0.42 nm) of the pseudo-hexagonal phase. The behaviour of these nylons is compared and contrasted with that of nylon 6 6, where only the c~-phase is found at room temperature and, on heating, the Brill temperature is found to occur in the range 95-35°C below the melting point at 265°C. ~, 1997 Elsevier Science Ltd.
Macromolecules, 1997
ABSTRACT Nylons 8 10 and 10 12 have been synthesized and crystallized as chain-folded lamellae fr... more ABSTRACT Nylons 8 10 and 10 12 have been synthesized and crystallized as chain-folded lamellae from 1,4-butanediol and the results compared with previous studies on Nylons 4 6 and 6 8. In 2N 2(N + 1) Nylons, the lengths of the two alkane segments are equal and two different hydrogen-bonded sheet schemes are possible: progressive or alternating shear. At room temperature, Nylons 8 10 and 10 12 adopt the progressive scheme and the adjacent re-entry folds in the crystals must be in the alkane chain segments. In contrast, Nylons 4 6 and 6 8 lamellae, crystallized from the same solvent, exhibit the alternating hydrogen bonding scheme and each adjacent re-entry fold must contain an amide group. The transition in the chemical nature of the lamellar surface, from the amide fold to the alkane fold, occurs in passing from Nylon 6 8 to 8 10. Thus, the progressive hydrogen-bonded sheet/alkane fold structure is energetically more favorable, provided the alkane-folding geometry is sufficiently relaxed; this comes with increasing alkane segment length. For each hydrogen-bonded sheet structure there are still two principal intersheet stacking modes in lamellar crystals: the progressively sheared α-phase or the alternatingly sheared β-phase, both of which have been found in the 8 10 and 10 12 Nylons. The 2N 2(N + 1) Nylons have the choice of four possible structures. The melting points of solution grown crystals of Nylons 4 6, 6 8, 8 10, and 10 12 decrease with decreasing intrachain amide density. When lamellar crystals of these Nylons are heated, the two characteristic interchain diffraction signals move together and meet at their Brill temperature; for Nylon 10 12 it appears to be close to the melting point.
Journal of Polymer Science Part B-polymer Physics, 1997
Four members of the even-even nylon 2 Y series, for Y Å 6, 8, 10, and 12, have been crystallized ... more Four members of the even-even nylon 2 Y series, for Y Å 6, 8, 10, and 12, have been crystallized in the form of chain-folded lamellar single crystals from 1,4butanediol and studied by transmission electron microscopy ( imaging and diffraction ) , x-ray diffraction, and thermal analysis. The structures of these 2 Y nylons are different from those of nylon 6 6 and many other even-even nylons. At room temperature, two strong diffraction signals are observed at spacings 0.42 and 0.39 nm, respectively; these values differ from the 0.44 and 0.37 nm diffraction signals observed for nylon 6 6 and most even-even nylons at ambient temperature. Detailed analyses of the diffraction patterns show that all these 2 Y nylons have triclinic unit cells. The diamine alkane segments of 2 Y nylons are too short to sustain chain folds; thus, the chain folds must be in the diacid alkane segments in all cases. On heating the crystals from room temperature to the melt, the triclinic structures transform into pseudohexagonal structures and the two diffraction signals meet at the Brill transition temperature which occurs significantly below the melting point. The room temperature structures of these 2 Y nylons are similar to the unit cell of nylon 6 6 at elevated temperature, but below its Brill temperature. The room temperature structures and behavior on heating of the nylon 2 Y family is noticeably different from that of the even-even nylon X 4 family, although the only difference between these families of polyamides is the relative disposition of the amide groups within the chains. The results show that in order to understand the structure, behavior and properties of crystalline nylons, especially as a function of temperature, the detailed stereochemistry needs to be taken into account.
Polymer, 1997
Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and... more Chain-folded single crystals of the seven even-even nylons: 4 8, 4 10, 4 12, 6 10, 6 12, 6 18 and 8 12 have been grown from solution and their morphologies and structures studied using transmission electron microscopy; both imaging and diffraction. Sedimented mats were examined using X-ray diffraction. The solution grown single crystals are lath-shaped lamellae. Diffraction from these crystals, at room temperature, reveals that three crystalline forms are commonly present. The crystals are composed of chain-folded, hydrogen-bonded sheets; the linear hydrogen bonds within the sheets generate a progressive shear of the chains. The sheets are found to stack in two different ways; some of the sheets stack with progressive shear, to form 'c~-phase' crystals; other sheets stack with alternate up and down stagger, to form ";7-phase' crystals. Both the c~-and ~3-crystals give two strong diffraction signals at spacings of 0.44 and 0.37 nm; these signals represent a projected inter-chain distance within a hydrogen-bonded sheet (actual value 0.48 nm) and the inter-sheet spacing, respectively. Some crystals also show an additional diffraction signal at 0.42 nm; this signal is characteristic of the pseudo-hexagonal phase, a phase usually only found at high temperatures. The melting points of solution grown crystals of this even-even nylon series decrease with decreasing linear density of hydrogen bonds. On heating, the strong diffraction signals in both c~-and/3-phases move together and meet, as is the case for other even-even nylons. The lowest temperature at which the two signals first have the same spacing is termed the Brill temperature. For all the nylons of the present study the Brill temperature is coincident with the melting temperature, and the two strong signals meet at the spacing (0.42 nm) of the pseudo-hexagonal phase. The behaviour of these nylons is compared and contrasted with that of nylon 6 6, where only the c~-phase is found at room temperature and, on heating, the Brill temperature is found to occur in the range 95-35°C below the melting point at 265°C. ~, 1997 Elsevier Science Ltd.
Estamos en un momento crítico de la historia de la Tierra, en el cual la humanidad debe elegir su... more Estamos en un momento crítico de la historia de la Tierra, en el cual la humanidad debe elegir su futuro. A medida que el mundo se vuelve cada vez más interdependiente y frágil, el futuro depara, a la vez, grandes riesgos y grandes promesas. Para seguir adelante, debemos reconocer que en medio de la magnífica diversidad de culturas y formas de vida, somos una sola familia humana y una sola comunidad terrestre con un destino común. Debemos unirnos para crear una sociedad global sostenible fundada en el respeto hacia la naturaleza, los derechos humanos universales, la justicia económica y una cultura de paz. En torno a este fin, es imperativo que nosotros, los pueblos de la Tierra, declaremos nuestra responsabilidad unos hacia otros, hacia la gran comunidad de la vida y hacia las generaciones futuras.