Yagi, M, Wolf KV, Baesjou PJ, Bernasek SL, Dismukes CG.  2001.  Selective Photoproduction of O2 from the Mn4O4 Cubane Core: A Structural and Functional Model for the Photosynthetic Water-Oxidizing Complex. Angewandte Chemie. 113:3009-3012.Website
Song, R, Llaca V, Linton E, Messing J.  2001.  Sequence, regulation, and evolution of the maize 22-kD alpha zein gene family. Genome research. 11:1817-25. AbstractWebsite
We have isolated and sequenced all 23 members of the 22-kD alpha zein (z1C) gene family of maize. This is one of the largest plant gene families that has been sequenced from a single genetic background and includes the largest contiguous genomic DNA from maize with 346,292 bp to date. Twenty-two of the z1C members are found in a roughly tandem array on chromosome 4S forming a dense gene cluster 168,489-bp long. The twenty-third copy of the gene family is also located on chromosome 4S at a site approximately 20 cM closer to the centromere and appears to be the wild-type allele of the floury-2 (fl2) mutation. On the basis of an analysis of maize cDNA databases, only seven of these genes appear to be expressed including the fl2 allele. The expressed genes in the cluster are interspersed with nonexpressed genes. Interestingly, some of the expressed genes differ in their transcriptional regulation. Gene amplification appears to be in blocks of genes explaining the rapid and compact expansion of the cluster during the evolution of maize.
Messing, J.  2001.  The universal primers and the shotgun DNA sequencing method. Methods in molecular biology (Clifton, NJ). 167:13-31.Website
Naryshkin, N, Kim Y, Dong Q, Ebright RH.  2001.  Site-specific protein-DNA photocrosslinking. Analysis of bacterial transcription initiation complexes.. Methods in molecular biology (Clifton, N.J.). 148:337-61.
Mukhopadhyay, J, Kapanidis AN, Mekler V, Kortkhonjia E, Ebright YW, Ebright RH.  2001.  Translocation of sigma(70) with RNA polymerase during transcription: fluorescence resonance energy transfer assay for movement relative to DNA.. Cell. 106(4):453-63. Abstract
Using fluorescence resonance energy transfer, we show that, in the majority of transcription complexes, sigma(70) is not released from RNA polymerase upon transition from initiation to elongation, but, instead, remains associated with RNA polymerase and translocates with RNA polymerase. The results argue against the presumption that there are necessary subunit-composition differences, and corresponding necessary mechanistic differences, in initiation and elongation. The methods of this report should be generalizable to monitor movement of any molecule relative to any nucleic acid.
Minakhin, L, Bhagat S, Brunning A, Campbell EA, Darst SA, Ebright RH, Severinov K.  2001.  Bacterial RNA polymerase subunit omega and eukaryotic RNA polymerase subunit RPB6 are sequence, structural, and functional homologs and promote RNA polymerase assembly.. Proceedings of the National Academy of Sciences of the United States of America. 98(3):892-7. Abstract
Bacterial DNA-dependent RNA polymerase (RNAP) has subunit composition beta'betaalpha(I)alpha(II)omega. The role of omega has been unclear. We show that omega is homologous in sequence and structure to RPB6, an essential subunit shared in eukaryotic RNAP I, II, and III. In Escherichia coli, overproduction of omega suppresses the assembly defect caused by substitution of residue 1362 of the largest subunit of RNAP, beta'. In yeast, overproduction of RPB6 suppresses the assembly defect caused by the equivalent substitution in the largest subunit of RNAP II, RPB1. High-resolution structural analysis of the omega-beta' interface in bacterial RNAP, and comparison with the RPB6-RPB1 interface in yeast RNAP II, confirms the structural relationship and suggests a "latching" mechanism for the role of omega and RPB6 in promoting RNAP assembly.
Chen, S, Gunasekera A, Zhang X, Kunkel TA, Ebright RH, Berman HM.  2001.  Indirect readout of DNA sequence at the primary-kink site in the CAP-DNA complex: alteration of DNA binding specificity through alteration of DNA kinking.. Journal of molecular biology. 314(1):75-82. Abstract
The catabolite activator protein (CAP) sharply bends DNA in the CAP-DNA complex, introducing a DNA kink, with a roll angle of approximately 40 degrees and a twist angle of approximately 20 degrees, between positions 6 and 7 of the DNA half-site, 5'-A(1)A(2)A(3)T(4)G(5)T(6)G(7)A(8)T(9)C(10)T(11)-3' ("primary kink"). CAP recognizes the base-pair immediately 5' to the primary-kink site, T:A(6), through an "indirect-readout" mechanism involving sequence effects on the energetics of primary-kink formation. CAP recognizes the base-pair immediately 3' to the primary-kink site, G:C(7), through a "direct-readout" mechanism involving formation of a hydrogen bond between Glu181 of CAP and G:C(7). Here, we report that substitution of the carboxylate side-chain of Glu181 of CAP by the one-methylene-group-shorter carboxylate side-chain of Asp changes DNA binding specificity at position 6 of the DNA half site, changing specificity for T:A(6) to specificity for C:G(6), and we report a crystallographic analysis defining the structural basis of the change in specificity. The Glu181-->Asp substitution eliminates the primary kink and thus eliminates indirect-readout-based specificity for T:A(6). The Glu181-->Asp substitution does not eliminate hydrogen-bond formation with G:C(7), and thus does not eliminate direct-readout-based specificity for G:C(7).
Chen, S, Vojtechovsky J, Parkinson GN, Ebright RH, Berman HM.  2001.  Indirect readout of DNA sequence at the primary-kink site in the CAP-DNA complex: DNA binding specificity based on energetics of DNA kinking.. Journal of molecular biology. 314(1):63-74. Abstract
The catabolite activator protein (CAP) makes no direct contact with the consensus base-pair T:A at position 6 of the DNA half-site 5'-A(1)A(2)A(3)T(4)G(5)T(6)G(7)A(8)T(9)C(10)T(11)-3' but, nevertheless, exhibits strong specificity for T:A at position 6. Binding of CAP results in formation of a sharp DNA kink, with a roll angle of approximately 40 degrees and a twist angle of approximately 20 degrees, between positions 6 and 7 of the DNA half-site. The consensus base-pair T:A at position 6 and the consensus base-pair G:C at position 7 form a T:A/G:C step, which is known to be associated with DNA flexibility. It has been proposed that specificity for T:A at position 6 is a consequence of formation of the DNA kink between positions 6 and 7, and of effects of the T:A(6)/G:C(7) step on the geometry of DNA kinking, or the energetics of DNA kinking. In this work, we determine crystallographic structures of CAP-DNA complexes having the consensus base-pair T:A at position 6 or the non-consensus base-pair C:G at position 6. We show that complexes containing T:A or C:G at position 6 exhibit similar overall DNA bend angles and local geometries of DNA kinking. We infer that indirect readout in this system does not involve differences in the geometry of DNA kinking but, rather, solely differences in the energetics of DNA kinking. We further infer that the main determinant of DNA conformation in this system is protein-DNA interaction, and not DNA sequence.
Kapanidis, AN, Ebright YW, Ludescher RD, Chan S, Ebright RH.  2001.  Mean DNA bend angle and distribution of DNA bend angles in the CAP-DNA complex in solution.. Journal of molecular biology. 312(3):453-68. Abstract
In order to define the mean DNA bend angle and distribution of DNA bend angles in the catabolite activator protein (CAP)-DNA complex in solution under standard transcription initiation conditions, we have performed nanosecond time-resolved fluorescence measurements quantifying energy transfer between a probe incorporated at a specific site in CAP, and a complementary probe incorporated at each of five specific sites in DNA. The results indicate that the mean DNA bend angle is 77(+/-3) degrees - consistent with the mean DNA bend angle observed in crystallographic structures (80(+/-12) degrees ). Lifetime-distribution analysis indicates that the distribution of DNA bend angles is relatively narrow, with <10 % of DNA bend angles exceeding 100 degrees. Millisecond time-resolved luminescence measurements using lanthanide-chelate probes provide independent evidence that the upper limit of the distribution of DNA bend angles is approximately 100 degrees. The methods used here will permit mutational analysis of CAP-induced DNA bending and the role of CAP-induced DNA bending in transcriptional activation.
Dismukes, GC.  2001.  Splitting Water. Science. 292:447-448.Website
Rongo, C.  2001.  Disparate cell types use a shared complex of PDZ proteins for polarized protein localization. Cytokine Growth Factor Rev. 12:349-59. AbstractWebsite
Based on their morphology and function, epithelial cells and neurons appear to have very little in common; however, growing evidence indicates that these two disparate cell types share an underlying polarization pathway responsible for sorting proteins to specific subcellular sites. An evolutionarily conserved complex of PDZ domain-containing proteins thought to be responsible for polarized protein localization has been identified from both brain and epithelial tissue, both from mammals and from the nematode C. elegans. Some of the most recent data on PDZ proteins and the proteins with which they interact are summarized. In particular, some of the more recently proposed models for their function in cells, and the in vivo and in vitro data that support these models are focussed upon.
Irvine, KD, Rauskolb C.  2001.  Boundaries in development: formation and function. Annual Review of Cell and Developmental Biology. 17:189-214. AbstractWebsite
Developing organisms may contain billions of cells destined to differentiate in numerous different ways. One strategy organisms use to simplify the orchestration of development is the separation of cell populations into distinct functional units. Our expanding knowledge of boundary formation and function in different systems is beginning to reveal general principles of this process. Fields of cells are subdivided by the interpretation of morphogen gradients, and these subdivisions are then maintained and refined by local cell-cell interactions. Sharp and stable separation between cell populations requires special mechanisms to keep cells segregated, which in many cases appear to involve the regulation of cell affinity. Once cell populations become distinct, specialized cells are often induced along the borders between them. These boundary cells can then influence the patterning of surrounding cells, which can result in progressively finer subdivisions of a tissue. Much has been learned about the signaling pathways that establish boundaries, but a key challenge for the future remains to elucidate the cellular and molecular mechanisms that actually keep cell populations separated.
Grammont, M, Irvine KD.  2001.  fringe and Notch specify polar cell fate during Drosophila oogenesis. Development (Cambridge, England). 128:2243-53. AbstractWebsite
fringe encodes a glycosyltransferase that modulates the ability of the Notch receptor to be activated by its ligands. We describe studies of fringe function during early stages of Drosophila oogenesis. Animals mutant for hypomorphic alleles of fringe contain follicles with an incorrect number of germline cells, which are separated by abnormally long and disorganized stalks. Analysis of clones of somatic cells mutant for a null allele of fringe localizes the requirement for fringe in follicle formation to the polar cells, and demonstrates that fringe is required for polar cell fate. Clones of cells mutant for Notch also lack polar cells and the requirement for Notch in follicle formation appears to map to the polar cells. Ectopic expression of fringe or of an activated form of Notch can generate an extra polar cell. Our results indicate that fringe plays a key role in positioning Notch activation during early oogenesis, and establish a function for the polar cells in separating germline cysts into individual follicles.
Koppen, M, Simske JS, Sims PA, Firestein BL, Hall DH, Radice AD, Rongo C, Hardin JD.  2001.  Cooperative regulation of AJM-1 controls junctional integrity in Caenorhabditis elegans epithelia. Nat Cell Biol. 3:983-91. AbstractWebsite
The function of epithelial cell sheets depends on the integrity of specialized cell-cell junctions that connect neighbouring cells. We have characterized the novel coiled-coil protein AJM-1, which localizes to an apical junctional domain of Caenorhabditis elegans epithelia basal to the HMR-HMP (cadherin-catenin) complex. In the absence of AJM-1, the integrity of this domain is compromised. Proper AJM-1 localization requires LET-413 and DLG-1, homologues of the Drosophila tumour suppressors Scribble and Discs large, respectively. DLG-1 physically interacts with AJM-1 and is required for its normal apical distribution, and LET-413 mediates the rapid accumulation of both DLG-1 and AJM-1 in the apical domain. In the absence of both dlg-1 and let-413 function AJM-1 is almost completely lost from apical junctions in embryos, whereas HMP-1 (alpha-catenin) localization is only mildly affected. We conclude that LET-413 and DLG-1 cooperatively control AJM-1 localization and that AJM-1 controls the integrity of a distinct apical junctional domain in C. elegans.
Firestein, BL, Rongo C.  2001.  DLG-1 is a MAGUK similar to SAP97 and is required for adherens junction formation. Mol Biol Cell. 12:3465-75. AbstractWebsite
Cellular junctions are critical for intercellular communication and for the assembly of cells into tissues. Cell junctions often consist of tight junctions, which form a permeability barrier and prevent the diffusion of lipids and proteins between cell compartments, and adherens junctions, which control the adhesion of cells and link cortical actin filaments to attachment sites on the plasma membrane. Proper tight junction formation and cell polarity require the function of membrane-associated guanylate kinases (MAGUKs) that contain the PDZ protein-protein interaction domain. In contrast, less is known about how adherens junctions are assembled. Here we describe how the PDZ-containing protein DLG-1 is required for the proper formation and function of adherens junctions in Caenorhabditis elegans. DLG-1 is a MAGUK protein that is most similar in sequence to mammalian SAP97, which is found at both synapses of the CNS, as well as at cell junctions of epithelia. DLG-1 is localized to adherens junctions, and DLG-1 localization is mediated by an amino-terminal domain shared with SAP97 but not found in other MAGUK family members. DLG-1 recruits other proteins and signaling molecules to adherens junctions, while embryos that lack DLG-1 fail to recruit the proteins AJM-1 and CPI-1 to adherens junctions. DLG-1 is required for the proper organization of the actin cytoskeleton and for the morphological elongation of embryos. In contrast to other proteins that have been observed to affect adherens junction assembly and function, DLG-1 is not required to maintain cell polarity. Our results suggest a new function for MAGUK proteins distinct from their role in cell polarity.
Padgett, RW, Patterson GI.  2001.  New developments for TGFβ. Developmental cell. 1:343-9. AbstractWebsite
A recent FASEB meeting was held in Tucson, Arizona that encompassed TGFbeta superfamily signaling pathways and their roles in development. This review focuses on the developmental biology presented at the meeting.
Giunta, KL, Jang JK, Manheim EM, Subramanian G, McKim KS.  2002.  subito encodes a kinesin-like protein required for meiotic spindle pole formation in Drosophila melanogaster. Genetics. 160:1489-1501.
Sheats, JE, Micai K, Bleier S, Storey D, Sellito E, Carrell TG, Maneiro M, Bourles E, Dismukes GC, Rheingold AL et al..  2002.  Assembly of manganese-oxo clusters in solution as models for the photosynthetic oxygen-evolving complex. Macromolecular Symposia. 186:29-34.Website
Montano, SP, Cot'e ML, Fingerman I, Pierce M, Vershon AK, Georgiadis MM.  2002.  Crystal Structure of the DNA-binding Domain from Ndt80, a Transcriptional Activator Required for Meiosis in Yeast. Proc Natl Acad Sci U S A. 99:14041-14046. Abstract
Ndt80 is a transcriptional activator required for meiosis in the yeast Saccharomyces cerevisiae. Here, we report the crystal structure at 2.3 A resolution of the DNA-binding domain of Ndt80 experimentally phased by using the anomalous and isomorphous signal from a single ordered Se atom per molecule of 272-aa residues. The structure reveals a single approximately 32-kDa domain with a distinct fold comprising a beta-sandwich core elaborated with seven additional beta-sheets and three short alpha-helices. Inspired by the structure, we have performed a mutational analysis and defined a DNA-binding motif in this domain. The DNA-binding domain of Ndt80 is homologous to a number of proteins from higher eukaryotes, and the residues that we have shown are required for DNA binding by Ndt80 are highly conserved among this group of proteins. These results suggest that Ndt80 is the defining member of a previously uncharacterized family of transcription factors, including the human protein (C11orf9), which has been shown to be highly expressed in invasive or metastatic tumor cells.
Montano, SP, Pierce M, Cot'e ML, Vershon AK, Georgiadis MM.  2002.  Crystallographic Studies of a Novel DNA-binding Domain from the Yeast Transcriptional Activator Ndt80. Acta Crystallogr D Biol Crystallogr. 58:2127-2130. Abstract
The Ndt80 protein is a transcriptional activator that plays a key role in the progression of the meiotic divisions in the yeast Saccharomyces cerevisiae. Ndt80 is strongly induced during the middle stages of the sporulation pathway and binds specifically to a promoter element called the MSE to activate transcription of genes required for the meiotic divisions. Here, the preliminary structural and functional studies to characterize the DNA-binding activity of this protein are reported. Through deletion analysis and limited proteolysis studies of Ndt80, a novel 32 kDa DNA-binding domain that is sufficient for DNA-binding in vitro has been defined. Crystals of the DNA-binding domain of Ndt80 in two distinct lattices have been obtained, for which diffraction data extend to 2.3 A resolution.
Manheim, EA, Jang JK, Dominic D, McKim KS.  2002.  Cytoplasmic localization and evolutionary conservation of MEI-218, a protein required for meiotic crossing over in Drosophila. Mol. Biol. Cell. 13:84-95.
Hart, B, Mathias JR, Ott D, McNaughton L, Anderson JS, Vershon AK, Baxter SM.  2002.  Engineered Improvements in DNA-binding Function of the MATa1 Homeodomain Reveal Structural Changes Involved in Combinatorial Control. J Mol Biol. 316:247-256. Abstract
We have engineered enhanced DNA-binding function into the a1 homeodomain by making changes in a loop distant from the DNA-binding surface. Comparison of the free and bound a1 structures suggested a mechanism linking van der Waals stacking changes in this loop to the ordering of a final turn in the DNA-binding helix of a1. Inspection of the protein sequence revealed striking differences in amino acid identity at positions 24 and 25 compared to related homeodomain proteins. These positions lie in the loop connecting helix-1 and helix-2, which is involved in heterodimerization with the alpha 2 protein. A series of single and double amino acid substitutions (a1-Q24R, a1-S25Y, a1-S25F and a1-Q24R/S25Y) were engineered, expressed and purified for biochemical and biophysical study. Calorimetric measurements and HSQC NMR spectra confirm that the engineered variants are folded and are equally or more stable than the wild-type a1 homeodomain. NMR analysis of a1-Q24R/S25Y demonstrates that the DNA recognition helix (helix-3) is extended by at least one turn as a result of the changes in the loop connecting helix-1 and helix-2. As shown by EMSA, the engineered variants bind DNA with enhanced affinity (16-fold) in the absence of the alpha 2 cofactor and the variant alpha 2/a1 heterodimers bind cognate DNA with specificity and affinity reflective of the enhanced a1 binding affinity. Importantly, in vivo assays demonstrate that the a1-Q24R/S25Y protein binds with fivefold greater affinity than wild-type a1 and is able to partially suppress defects in repression by alpha 2 mutants. As a result of these studies, we show how subtle differences in residues at a surface distant from the functional site code for a conformational switch that allows the a1 homeodomain to become active in DNA binding in association with its cofactor alpha 2.