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M Granger-Schnarr

Publications and source records attributed to M Granger-Schnarr.

At least 19 recordsLinked to original sources
PubMed1998

A LexA mutant repressor with a relaxed inter-domain linker.

The LexA protein is part of a large family of prokaryotic transcriptional repressors that contain an amino-terminal DNA binding domain and a carboxy-terminal dimerization domain. These domains are separated by a linker or hinge region, which is generally considered to be rather flexible and unconstrained. So far, no structure of any of the full-length repressors is available. Here we show that a mutant LexA repressor harboring several point mutations in the hinge region gets sensitive to trypsin and Glu-C cleavage over a segment of at least 20 amino acids, whereas the LexA wild-type hinge region is resistant to these proteases. These data are not compatible with the hypothesis of an fully flexible and/or unstructured inter-domain linker and suggest that the LexA hinge region is, in fact, constrained by contacts with the carboxy-terminal domain and/or a fairly stable local structure of the linker region.

Amino Acid Sequence↗
PubMed1998

A new LexA-based genetic system for monitoring and analyzing protein heterodimerization in Escherichia coli.

Interactions between proteins affect a wide variety of biological processes, such as signal transduction and control of gene expression. In order to facilitate the study of protein-protein interactions we have developed a new method for specifically detecting the heterodimerization of two heterologous proteins in the bacterium Escherichia coli. The assay is based on the simultaneous use of protein fusions with an altered specificity and a wild-type LexA repressor DNA-binding domain. We have tested this system with two well known eukaryotic dimerization domains (the Fos and Jun leucine zippers). The two interacting proteins were, respectively, fused to a wild-type and a mutant LexA DNA-binding domain. Their hetero-association is specifically measured by the transcriptional repression of a reporter gene (lacZ) controlled by a hybrid operator containing a wild-type half-site (CTGT) and a mutated operator half-site (CCGT). The hybrid operator/lacZ construct was integrated into the chromosome of the reporter strain (SU202) to avoid possible artefacts due to variations in plasmid copy number. This method should be particularly useful in those cases where one or both partners are also able to form homodimers, since the assay described here is sensitive only to the formation of heterodimers. Furthermore, this assay gives rise to a screenable red/white phenotype on MacConkey-lactose indicator plates, allowing for a genetic study of the specificity of the interaction.

Bacterial Proteins↗
PubMed1997

DNA binding and transactivation properties of Fos variants with homodimerization capacity.

The mammalian Fos and Fos-related proteins are unable to form homodimers and to bind DNA in the absence of a second protein, like c-Jun for example. In order to study the implications of hydrophobic point mutations in the c-Fox leucine zipper on DNA binding of the entire c-Fos protein, we have constructed and purified a set of Fos mutant proteins harboring one or several isoleucine or leucine residues in the five Fos zipper a positions. We show that a single point mutation in the hydrophobic interface of the c-Fos leucine zipper enables the c-Fos mutant protein to bind specifically to an oligonucleotide duplex harboring the TRE consensus sequence TGA(C/G)TCA. This point mutation (Thr196-->Ile) is situated in the a position of the second heptade (a2) of the Fos zipper. The introduction of additional isoleucine residues in the other a positions progressively increases the DNA binding affinity of these homodimerizing Fos zipper variants. Heterodimerization of these c-Fos variants with c-Jun reveals a complex behavior, in that the DNA binding affinity of these heterodimers does not simply increase with the number of isoleucine side chains in position a. For example, a c-Fos variant harboring a wild-type Thr in position a1 aad Ile in the four other a positions (c-Fos4I) interacts more tightly with c-Jun than a variant harboring Ile in all five a positions (c-Fos5I). The same holds true for the corresponding leucine variants, suggesting that the wild-type a1 residue of the Fox zipper (Thr162) is thermodynamically relevant for Fos-Jun heterodimer formations and DNA binding. The c-Fos4I variant forms heterodimers with c-Jun slightly better than the wild-type zipper protein, suggesting that the driving force for Fos-Jun heterodimerization is not the simple fact that the Fos protein is unable to form homodimers. These c-Fos variants were further tested for their transactivation properties in F9 and NIH3T3 cells. At low expression levels the most efficiently homodimerizing variant (c-Fos5I) activates transcription in F9 cells about 6-fold. However part of this activation may be due to the formation of heterodimers with a member of the Jun family (like JunD for example), since a wild type c-Fos expression vector confers a 3-fold activation under these conditions. In the case of the homodimerizing c-Fos variants however, this activation is abrogated at higher expression levels due to a strong inhibition of basal transcription activity.

3T3 Cells↗
PubMed1996

Nucleosome assembly on the human c-fos promoter interferes with transcription factor binding.

cAMP-responsive-element (CRE)-binding factors interaction with nucleosomal DNA has been investigated in vitro on the human c-fos promoter. Analysis of nucleosome reconstitution of this promoter shows a preferential nucleosome positioning on the proximal promoter sequences, including the CRE centered at -60 relative to the start site of transcription. CRE-binding protein (CREB) and modulator protein (CREM) are unable to interact with their recognition site incorporated in a nucleosome. However, competition between transcription factor binding and nucleosome assembly allows CREM binding and induces important modifications in the nucleosomal structure suggesting the displacement of nucleosomes. These findings imply that binding of transcription factors to the CRE prior to cAMP induction might be required to prevent the incorporation of this element in a nucleosome.

Base Sequence↗
PubMed1996

DNA binding of Jun and Fos bZip domains: homodimers and heterodimers induce a DNA conformational change in solution.

We constructed plasmids encoding the sequences for the bZip modules of c-Jun and c-Fos which could then be expressed as soluble proteins in Escherichia coli. The purified bZip modules were tested for their binding capacities of synthetic oligonucleotides containing either TRE or CRE recognition sites in electrophoretic mobility shift assays and circular dichroism (CD). Electrophoretic mobility shift assays showed that bZip Jun homodimers and bZip Jun/Fos heterodimers bind a collagenase-like TRE (CTGACTCAT) with dissociation constants of respectively 1.4 x 10(-7) M and 5 x 10(-8) M. As reported earlier [Patel et al. (1990) Nature 347, 572-575], DNA binding induces a marked change of the protein structure. However, we found that the DNA also undergoes a conformational change. This is most clearly seen with small oligonucleotides of 13 or 14 bp harboring respectively a TRE (TGACTCA) or a CRE (TGACGTCA) sequence. In this case, the positive DNA CD signal at 280 nm increases almost two-fold with a concomitant blue-shift of 3-4 nm. Within experimental error the same spectral changes are observed for TRE and CRE containing DNA fragments. The spectral changes observed with a non-specific DNA fragment are weaker and the signal of free DNA is recovered upon addition of much smaller salt concentrations than required for a specific DNA fragment. Surprisingly the spectral changes induced by Jun/Jun homodimers are not identical to those induced by Jun/Fos heterodimers. However, in both cases the increase of the positive CD band and the concomitant blue shift would be compatible with a B to A-transition of part of the binding site or a DNA conformation intermediate between the canonical A and B structures.

Amino Acid Sequence↗
PubMed1996

Structure of the LexA repressor-DNA complex probed by affinity cleavage and affinity photo-cross-linking.

The structure of the complex of full-length Escherichia coli LexA repressor with a consensus operator DNA fragment has been probed by affinity photo-cross-linking and affinity cleavage. These methods allow the determination of approximate intermolecular distances between a given protein residue and a base or sugar moiety within the operator. In a first step unique cysteine residues were introduced in positions 7, 28, 38, or 52 of the protein. In all four cases, the original amino acid was an arginine. The four amino acids in these positions were expected to be situated on the surface of LexA interacting with DNA, as inferred from the structure of the LexA DNA binding domain [Fogh et al. (1994) EMBO J. 13, 3936-3944]. In a second step, these unique cysteine side chains of the purified proteins were chemically modified either with 4-azidophenacyl bromide or with S-(2-pyridylthio)cysteaminyl-EDTA. The first set of derivatives gives rise to UV-induced cross-linking which may be revealed by alkali/heat treatment; the second leads to direct DNA cleavage in the proximity of the derivatized amino acid. To reduce hydroxyl radical diffusion, the EDTA-iron cleavage reactions were done in the presence of high amounts of glycerol. The results indicate that amino acids 7 and 52 are near nucleotide pairs 8-12 of the operator and that amino acids 28 and 36 of LexA are near nucleotide pairs 5-8 of the operator. The results unambiguously define the orientation of the LexA DNA binding domain relative to the operator and provide support for the model of the LexA-operator complex proposed by Knegtel et al. [(1995) Proteins 21, 226-236]. Ethylation interference experiments further suggest that Arg-7 contacts the phosphate group between nucleotides 8 and 9 as predicted by the model.

Affinity Labels↗
PubMed1995

Fos leucine zipper variants with increased association capacity.

The Fos wild-type leucine zipper is unable to support homodimerization. This finding is generally explained by the negative net charge of the Fos zipper leading to the electrostatic repulsion of two monomers. Using a LexA-dependent in vivo assay in Escherichia coli, we show here that additional antideterminants for Fos zipper association are the residues in position a within the Fos zipper interface. If the wild-type Fos zipper is fused to the DNA binding domain of the LexA repressor (LexA-DBD), no excess repression is observed as compared with the LexA-DBD alone, in agreement with the incapacity of the wild-type Fos zipper to promote homodimerization. If hydrophobic amino acids (Ile, Leu, Val, Phe, Met) are inserted into the five a positions of a LexA-Fos zipper fusion protein, substantial transcriptional repression is recovered showing that Fos zipper homodimerization is not only limited by the repulsion of negatively charged residues but also by the nonhydrophobic nature of the a positions. The most efficient variants (harboring Ile or Leu in the five a positions) show an about 80-fold increase in transcriptional repression as compared with the wild-type Fos zipper fusion protein. In the case of multiple identical substitutions, the overall improvement is correlated with the hydrophobicity of the inserted side chains, i.e. Ile Leu > Val > Phe > Met. However at least for Val, Phe, and Met the impact of a given residue type on the association efficiency depends strongly on the heptad, i.e. on the local environment of the a residue. This is particularly striking for the second heptad of the Fos zipper, where Val is less well tolerated than Phe and Met. Most likely the a1 residue modulates the interhelical repulsion between two glutamic acid side chains in positions g1 and e2. Most of the hydrophobic Fos zipper variants are also improved in heteroassociation with a Jun leucine zipper, such that roughly half of the additional free energy of homodimerization is imported into the heterodimer. A few candidates (including the Fos wild-type zipper) deviate from this correlation, showing considerable excess heteroassociation.

3T3 Cells↗
PubMed1994

Two pairs of oppositely charged amino acids from Jun and Fos confer heterodimerization to GCN4 leucine zipper.

The preferential assembly of Jun and Fos into heterodimers has been shown to be mainly driven by 16 amino acids (8 from each protein) situated in positions e and g of the leucine zipper coiled-coil structures of the two proteins (O'Shea, E. K., Rutkowski, R., and Kim, P. S. (1992) Cell 68, 699-708). Using a similar approach, we show that among these residues two pairs of oppositely charged amino acids account in fact for most of the additional free energy of heterodimerization in this system. These residues are 2 glutamic acid side chains in positions g1 and e2 of the Fos leucine zipper and 2 lysine residues in the equivalent positions of the Jun zipper. These amino acids were placed in the context of a GCN4 leucine zipper using peptide synthesis. These peptides contain unique cysteine residues enabling the formation of covalent dimers. The gain in heterodimer free energy has been determined both by cysteine-linked dimer formation under redox conditions and by thermal melting experiments of covalent dimers using circular dichroism experiments. The two pairs of oppositely charged residues (Glu,Glu and Lys,Lys) in positions g1 and e2 contribute at least -1.9 kcal/mol of additional free energy, accounting for a 50-fold excess of the heterodimer with respect to one of the homodimers. Thermal denaturation studies as a function of pH and ionic strength suggest that electrostatic effects should indeed be a major driving force for heterodimerization. On the contrary, peptides harboring the 12 amino acids from Jun and Fos in the other e and g positions (i.e. in e1, g2, e3, g3, e4, and g4) show only a moderate tendency to form heterodimers.

Amino Acid Sequence↗
PubMed1994

Phosphorylation of Escherichia coli proteins during the SOS response.

1. The phosphorylation of Escherichia coli proteins was analyzed comparatively before and after induction of the SOS response in a temperature-sensitive mutant strain. 2. The presence of phosphorylated proteins was evidenced by gel electrophoresis and autoradiography after labelling with radioactive orthophosphate in vivo or radioactive adenosine triphosphate in vitro. 3. Significant changes in the intensity of protein labelling were observed upon induction of the SOS functions: six proteins were found to be more phosphorylated while two others were less phosphorylated. Moreover, five additional proteins appeared to become phosphorylated exclusively during the SOS response. The molecular mass and isoelectric point of these various proteins were determined. 4. For most proteins, the changes in the pattern of protein phosphorylation were concomitant with variations in the amount of protein synthesized. 5. The changes in the pattern of phosphoproteins observed during the SOS response were not due to the temperature shift required experimentally for expressing the SOS phenotype. 6. Phosphorylation was found to be catalyzed by protein kinases that modify amino acid residues at hydroxyl groups in protein substrates. 7. Both in vivo and in vitro studies brought evidence that neither RecA nor LexA, the two key regulatory proteins of the SOS functions, were capable of undergoing phosphorylation.

Bacterial Proteins↗
PubMed1993

DNA sequence determinants of LexA-induced DNA bending.

The LexA repressor from Escherichia coli induces DNA bending upon interaction with the two overlapping operators which regulate the transcription of the colicin A encoding gene caa. Both caa operators harbor T-tracts adjacent to their recognition motifs. These tracts have been suggested to be especially favorable for the promotion of LexA-induced DNA bending. Here we show that this is indeed the case, since disruption of the TTTT-tract adjacent to operator O1 by the replacement of the two central thymine bases by AA, GA or CG markedly reduces LexA-induced DNA bending. Simple A.T-richness in this position is thus not sufficient to promote full LexA-induced bending, albeit a TAAT sequence is always more efficient to promote bending than those sequences containing one or two C/G base pairs.

Bacterial Proteins↗
PubMed1993

Orientation of the LexA DNA-binding motif on operator DNA as inferred from cysteine-mediated phenyl azide crosslinking.

To address the question how the recognition helix of the LexA repressor is positioned within the major groove of operator DNA we have applied a site-specific photocrosslinking approach using a LexA mutant repressor (LexA-C52) that harbors a single cysteine side chain in position 52, close to the COOH terminus of helix 3. The LexA-C52 mutant repressor has been purified and modified site-specifically with the photoreactive azido compound 4-azidophenacyl bromide, giving rise to LexA-C52*. Here we show that LexA-C52* may be selectively photocrosslinked with two adjacent bases within each operator half-site. The crosslinked bases are located, respectively, 10 and 11 base pairs from the dyad axis of the operator. The crosslinking data imply that the LexA recognition helix is oriented opposite to what is generally observed for helix-turn-helix proteins and that this helix should form a steeper angle with respect to the plane of the base pairs than is observed for standard helix-turn-helix proteins.

Azides↗
PubMed1993

Spacing requirements between LexA operator half-sites can be relaxed by fusing the LexA DNA binding domain with some alternative dimerization domains.

The dimerization domain of the LexA repressor has been replaced by two heterologous dimerization motifs: the "leucine zipper" from the jun oncogene product and the carboxy-terminal oligomerization domain of Escherichia coli lac repressor. The corresponding hybrid proteins LexA1-87-Jun zipper and LexA1-87-lac repressor have been purified and their DNA binding properties have been studied using gel mobility shift assays. Both fusion proteins form stable specific complexes with a short DNA duplex harboring the CTGT(at)4ACAG consensus sequence of the LexA repressor. This conserved DNA binding capacity distinguishes these two fusion proteins from many others containing a LexA DNA binding domain fused to different heterologous transactivation and/or dimerization domains. However the fusion proteins LexA1-87-Jun zipper and LexA1-87-lac repressor behave differently from native LexA repressor in that these fusion proteins tolerate the insertion of additional base-pairs between the two invertedly repeated CTGT motifs. LexA1-87-Jun zipper requires two CTGT motifs and tolerates the insertion of at least two additional base-pairs between these motifs, whereas LexA1-87-lac repressor requires in fact only a single CTGT motif for the formation of a specific complex detectable in gel mobility shift assays. The inability of the normal LexA repressor to form well-defined complexes with operators containing additional base-pairs in the center suggests that the LexA "hinge region" between the amino-terminal DNA binding and the carboxy-terminal dimerization domain might not be entirely flexible. In an attempt to remove a hypothetical interaction between the LexA cleavage site (which is situated within the hinge region) and the catalytic cleavage center (situated within the carboxy-terminal domain) a LexA mutant repressor containing five simultaneous mutations in the hinge region has been constructed and purified. Surprisingly this mutant repressor failed to form stable complexes detectable by the gel mobility shift assay even with the normal consensus sequence, suggesting that the LexA hinge region is more than a simple connector between the two structural domains and that its chemical nature is important not only for LexA cleavage, but also for the formation of stable LexA-DNA complexes.

Avian Proteins↗
PubMed1992

Isolation and characterization of LexA mutant repressors with enhanced DNA binding affinity.

The LexA repressor from Escherichia coli is a sequence-specific DNA binding protein that shows no pronounced sequence homology with any of the known structural motifs involved in DNA binding. Since little is known about how this protein interacts with DNA, we have selected and characterized a great number of intragenic, second-site mutations which restored at least partially the activity of LexA mutant repressors deficient in DNA binding. In 47 cases, the suppressor effect of these mutations was due to an Ind- phenotype leading presumably to a stabilization of the mutant protein. With one exception, these second-site mutations are all found in a small cluster (amino acid residues 80 to 85) including the LexA cleavage site between amino acid residues 84 and 85 and include both already known Ind- mutations as well as new variants like GN80, GS80, VL82 and AV84. The remaining 26 independently isolated second-site suppressor mutations all mapped within the amino-terminal DNA binding domain of LexA, at positions 22 (situated in the turn between helix 1 and helix 2) and positions 57, 59, 62, 71 and 73. These latter amino acid residues are all found beyond helix 3, in a region where we have previously identified a cluster of LexA (Def) mutant repressors. In several cases the parental LexA (Def) mutation has been removed by subcloning or site-directed mutagenesis. With one exception, these LexA variants show tighter in vivo repression than the LexA wild-type repressor. The most strongly improved variant (LexA EK71, i.e. Glu71----Lys) that shows an about threefold increased repression rate in vivo, was purified and its binding to a short consensus operator DNA fragment studied using a modified nitrocellulose filter binding assay. As expected from the in vivo data, LexA EK71 interacts more tightly with both operator and (more dramatically) with non-operator DNA. A determination of the equilibrium association constants of LexA EK71 and LexA wild-type as a function of monovalent salt concentration suggests that LexA EK71 might form an additional ionic interaction with operator DNA as compared to the LexA wild-type repressor. A comparison of the binding of LexA to a non-operator DNA fragment further shows that LexA interacts with the consensus operator very selectively with a specificity factor of Ks/Kns of 1.4 x 10(6) under near-physiological salt conditions.

Amino Acid Sequence↗
PubMed1992

Transformation and transactivation suppressor activity of the c-Jun leucine zipper fused to a bacterial repressor.

Transcription factor c-Jun appears to be a nuclear target of the Ras-induced signal transduction pathway. In fact, some experiments show that transforming forms of the Ras protein cooperate with Jun in transcriptional activation mediated by an AP-1 site and others indicate that the two oncoproteins cooperate in cellular transformation. Although it is likely that intracellular signaling systems activated by Ras might act directly on c-Jun by inducing specific phosphorylation, it is unclear how c-Jun participates in the transformation process. Here, we present results obtained with a LexA-Jun zipper fusion that lacks both the transcriptional activation domains and the basic region of the DNA-binding domain of c-Jun and contains only the intact leucine-zipper domain. This fusion product has a dominant negative effect on the transcriptional activation elicited by phorbol esters, c-Jun, c-Fos, Ras and E1A on an AP-1-responsive site. An analogous LexA-Fos zipper fusion has similar effects on transcriptional induction. The LexA-Jun zipper fusion acts further as a transformation suppressor, since it causes the generation of nontransformed revertants of ras-transformed cells. This effect is likely to be elicited by the dimerization potential of the Jun leucine zipper trapping cellular Jun and/or Fos in a protein complex unable to bind to DNA. These data implicate further that Ras-mediated transformation involves functional transcription factor AP-1 and that it is possible to interfere with cell transformation by interfering simply with the dimerization of transcription factors involved in the transformation process.

3T3 Cells↗
PubMed1991

Construction, purification, and characterization of a hybrid protein comprising the DNA binding domain of the LexA repressor and the Jun leucine zipper: a circular dichroism and mutagenesis study.

An increasing number of eukaryotic transcription factors interacting specifically with DNA comprise a dimerization motif called the "leucine zipper". These leucine zipper proteins form homodimers and/or heterodimers with another protein containing a leucine zipper motif. The leucine zipper of the oncoprotein Jun is particular in that Jun may form homodimers as well as heterodimers with the oncoprotein Fos, which are however more stable than the Jun-Jun homodimers. Leucine zipper dimerization is thought to occur through a coiled-coil arrangement of parallel alpha-helices, but the rules governing the specificity of homo- and/or heterodimerization are still largely unknown. To address this question in the case of the Jun leucine zipper, we constructed a fusion protein containing the amino-terminal DNA binding domain of the LexA repressor from Escherichia coli fused to the Jun leucine zipper. This hybrid protein (LexA-JunZip) is stable in E. coli and confers much tighter repression in vivo than the DNA binding domain of LexA alone. DNA binding competition experiments with synthetic Jun and Fos leucine zipper peptides in vitro showed that the leucine zipper mediated dimerization of LexA-JunZip is essential for DNA binding of the fusion protein. The purified LexA-JunZip protein dimerizes in vitro with a dimerization constant of 2 x 10(7) M-1 at 5 degrees C. Dimerization is very sensitive to temperature, since the dimerization constant drops at 20 degrees C to 2 x 10(6) M-1 and at 30 degrees C to only 3 x 10(5) M-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1991

Interaction of a regulatory protein with a DNA target containing two overlapping binding sites.

The LexA repressor from Escherichia coli regulates the transcription of about 20 different genes upon binding to single or multiple operators. In this work we study the interaction of LexA with the control region of the caa gene (coding for the bacterial toxin colicin A) that contains two operators (O1 and O2) which overlap by at least 2 base pairs relevant for sequence specific DNA recognition. This arrangement raises the question of how the LexA molecules which bind to the central overlapping part of the two operators avoid steric clashes and further, of whether the interaction of LexA with the two operators is cooperative or not. To address these questions we have constructed two mutant operators (O1+O2- and O1-O2+) for which the two most strongly conserved base pairs in each of the external operator half-sites have been mutated. Using methylation interference with the complex formation of LexA with the wild-type and these two mutant operators we could show: 1) that the two mutant operators behave symmetrically in that the methylation of one crucial guanine base in both operator half-sites interferes strongly with complex formation, 2) but that in the wild-type operator (containing four functional operator half-sites) only the two external half-operators give rise to interference if this crucial guanine base is methylated, whereas methylation of the two equivalent guanine bases within the two central (overlapping) operator half-sites does not lead to interference with the formation of a complex where both operators are occupied simultaneously. These data suggest that the centrally bound LexA molecules adopt a somewhat different binding mode than those bound to the external half-operators in order to avoid steric clashes and/or to optimize protein-protein contacts which are likely to be at the origin of the binding cooperativity that we could demonstrate by quantitative DNase I footprinting and gel retardation experiments. While the methylation interference experiments revealed a non-equivalence for the binding of externally and centrally bound LexA molecules, both methylation protection and hydroxyl radical footprinting were unable to reveal this difference, suggesting that the difference between the two binding modes should be fairly subtle.

Bacterial Proteins↗
PubMed1991

DNA binding properties of the LexA repressor.

The LexA repressor from Escherichia coli negatively regulates the transcription of about 20 different genes upon binding with variable affinity to single-, double- or even triple-operators as in the case of the recN gene. Binding of LexA to multiple operators is cooperative if the spacing between these operators is favorable. LexA recognizes DNA via its amino-terminal domain. The three-dimensional structure of this domain has been determined by NMR measurements. It contains three alpha-helices spanning residues 8-20, 28-35 and 41-54. In view of this structure, but also according to homology considerations and the unusual contact pattern with the DNA backbone, the LexA repressor is not a normal helix-turn-helix DNA binding protein like for example phage lambda repressor. LexA is at best a distant relative of this class of transcription factors and should probably be considered as a protein that contains a new DNA binding motif. A cluster of LexA mutant repressors deficient in DNA binding falling into the third helix (residues 41-54 bp) suggests that this helix is involved in DNA recognition.

Amino Acid Sequence↗