1
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Abstract
We have created a bacterial semisynthetic organism (SSO) that retains an unnatural base pair (UBP) in its DNA, transcribes it into mRNA and tRNA with cognate unnatural codons and anticodons, and after the tRNA is charged with a noncanonical amino acid synthesizes proteins containing the noncanonical amino acid. Here, we report the first progress toward the creation of eukaryotic SSOs. After demonstrating proof-of-concept with human HEK293 cells, we show that a variety of different unnatural codon-anticodon pairs can efficiently mediate the synthesis of unnatural proteins in CHO cells. Interestingly, we find that there are both similarities and significant differences between how the prokaryotic and eukaryotic ribosomes recognize the UBP, with the eukaryotic ribosome appearing more tolerant. The results represent the first progress toward eukaryotic SSOs and, in fact, suggest that such SSOs might be able to retain more unnatural information than their bacterial counterparts.
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Affiliation(s)
- Anne Xiao-Zhou Zhou
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Kai Sheng
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Aaron W. Feldman
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, United States
| | - Floyd E. Romesberg
- Department of Chemistry, The Scripps Research Institute, La Jolla, CA 92037, United States
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2
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Feldman AW, Dien VT, Karadeema RJ, Fischer EC, You Y, Anderson BA, Krishnamurthy R, Chen JS, Li L, Romesberg FE. Optimization of Replication, Transcription, and Translation in a Semi-Synthetic Organism. J Am Chem Soc 2019; 141:10644-10653. [PMID: 31241334 DOI: 10.1021/jacs.9b02075] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Previously, we reported the creation of a semi-synthetic organism (SSO) that stores and retrieves increased information by virtue of stably maintaining an unnatural base pair (UBP) in its DNA, transcribing the corresponding unnatural nucleotides into the codons and anticodons of mRNAs and tRNAs, and then using them to produce proteins containing noncanonical amino acids (ncAAs). Here we report a systematic extension of the effort to optimize the SSO by exploring a variety of deoxy- and ribonucleotide analogues. Importantly, this includes the first in vivo structure-activity relationship (SAR) analysis of unnatural ribonucleoside triphosphates. Similarities and differences between how DNA and RNA polymerases recognize the unnatural nucleotides were observed, and remarkably, we found that a wide variety of unnatural ribonucleotides can be efficiently transcribed into RNA and then productively and selectively paired at the ribosome to mediate the synthesis of proteins with ncAAs. The results extend previous studies, demonstrating that nucleotides bearing no significant structural or functional homology to the natural nucleotides can be efficiently and selectively paired during replication, to include each step of the entire process of information storage and retrieval. From a practical perspective, the results identify the most optimal UBP for replication and transcription, as well as the most optimal unnatural ribonucleoside triphosphates for transcription and translation. The optimized SSO is now, for the first time, able to efficiently produce proteins containing multiple, proximal ncAAs.
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Affiliation(s)
- Aaron W Feldman
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Vivian T Dien
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Rebekah J Karadeema
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Emil C Fischer
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Yanbo You
- School of Chemistry and Chemical Engineering , Henan Normal University , Henan 453007 , P. R. China
| | - Brooke A Anderson
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Ramanarayanan Krishnamurthy
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Jason S Chen
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
| | - Lingjun Li
- School of Chemistry and Chemical Engineering , Henan Normal University , Henan 453007 , P. R. China
| | - Floyd E Romesberg
- Department of Chemistry , The Scripps Research Institute , 10550 North Torrey Pines Road , La Jolla , California 92037 , United States
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3
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Dien VT, Holcomb M, Feldman AW, Fischer EC, Dwyer TJ, Romesberg FE. Progress Toward a Semi-Synthetic Organism with an Unrestricted Expanded Genetic Alphabet. J Am Chem Soc 2018; 140:16115-16123. [PMID: 30418780 DOI: 10.1021/jacs.8b08416] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
We have developed a family of unnatural base pairs (UBPs), exemplified by the pair formed between dNaM and dTPT3, for which pairing is mediated not by complementary hydrogen bonding but by hydrophobic and packing forces. These UBPs enabled the creation of the first semisynthetic organisms (SSOs) that store increased genetic information and use it to produce proteins containing noncanonical amino acids. However, retention of the UBPs was poor in some sequence contexts. Here, to optimize the SSO, we synthesize two novel benzothiophene-based dNaM analogs, dPTMO and dMTMO, and characterize the corresponding UBPs, dPTMO-dTPT3 and dMTMO-dTPT3. We demonstrate that these UBPs perform similarly to, or slightly worse than, dNaM-dTPT3 in vitro. However, in the in vivo environment of an SSO, retention of dMTMO-dTPT3, and especially dPTMO-dTPT3, is significantly higher than that of dNaM-dTPT3. This more optimal in vivo retention results from better replication, as opposed to more efficient import of the requisite unnatural nucleoside triphosphates. Modeling studies suggest that the more optimal replication results from specific internucleobase interactions mediated by the thiophene sulfur atoms. Finally, we show that dMTMO and dPTMO efficiently template the transcription of RNA containing TPT3 and that their improved retention in DNA results in more efficient production of proteins with noncanonical amino acids. This is the first instance of using performance within the SSO as part of the UBP evaluation and optimization process. From a general perspective, the results demonstrate the importance of evaluating synthetic biology "parts" in their in vivo context and further demonstrate the ability of hydrophobic and packing interactions to replace the complementary hydrogen bonding that underlies the replication of natural base pairs. From a more practical perspective, the identification of dMTMO-dTPT3 and especially dPTMO-dTPT3 represents significant progress toward the development of SSOs with an unrestricted ability to store and retrieve increased information.
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Affiliation(s)
- Vivian T Dien
- Department of Chemistry , The Scripps Research Institute , La Jolla , California 92037 United States
| | - Matthew Holcomb
- Department of Chemistry , The Scripps Research Institute , La Jolla , California 92037 United States
| | - Aaron W Feldman
- Department of Chemistry , The Scripps Research Institute , La Jolla , California 92037 United States
| | - Emil C Fischer
- Department of Chemistry , The Scripps Research Institute , La Jolla , California 92037 United States
| | - Tammy J Dwyer
- Department of Chemistry and Biochemistry , University of San Diego , San Diego , California 92110 , United States
| | - Floyd E Romesberg
- Department of Chemistry , The Scripps Research Institute , La Jolla , California 92037 United States
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4
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Abstract
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The information available to any organism is encoded in a four
nucleotide, two base pair genetic code. Since its earliest days, the
field of synthetic biology has endeavored to impart organisms with
novel attributes and functions, and perhaps the most fundamental approach
to this goal is the creation of a fifth and sixth nucleotide that
pair to form a third, unnatural base pair (UBP) and thus allow for
the storage and retrieval of increased information. Achieving this
goal, by definition, requires synthetic chemistry to create unnatural
nucleotides and a medicinal chemistry-like approach to guide their
optimization. With this perspective, almost 20 years ago we began
designing unnatural nucleotides with the ultimate goal of developing
UBPs that function in vivo, and thus serve as the
foundation of semi-synthetic organisms (SSOs) capable of storing and
retrieving increased information. From the beginning, our efforts
focused on the development of nucleotides that bear predominantly
hydrophobic nucleobases and thus that pair not based on the complementary
hydrogen bonds that are so prominent among the natural base pairs
but rather via hydrophobic and packing interactions. It was envisioned
that such a pairing mechanism would provide a basal level of selectivity
against pairing with natural nucleotides, which we expected would
be the greatest challenge; however, this choice mandated starting
with analogs that have little or no homology to their natural counterparts
and that, perhaps not surprisingly, performed poorly. Progress toward
their optimization was driven by the construction of structure–activity
relationships, initially from in vitro steady-state
kinetic analysis, then later from pre-steady-state and PCR-based assays,
and ultimately from performance in vivo, with the
results augmented three times with screens that explored combinations
of the unnatural nucleotides that were too numerous to fully characterize
individually. The structure–activity relationship data identified
multiple features required by the UBP, and perhaps most prominent
among them was a substituent ortho to the glycosidic linkage that
is capable of both hydrophobic packing and hydrogen bonding, and nucleobases
that stably stack with flanking natural nucleobases in lieu of the potentially more stabilizing stacking interactions afforded
by cross strand intercalation. Most importantly, after the examination
of hundreds of unnatural nucleotides and thousands of candidate UBPs,
the efforts ultimately resulted in the identification of a family
of UBPs that are well recognized by DNA polymerases when incorporated
into DNA and that have been used to create SSOs that store and retrieve
increased information. In addition to achieving a longstanding goal
of synthetic biology, the results have important implications for
our understanding of both the molecules and forces that can underlie
biological processes, so long considered the purview of molecules
benefiting from eons of evolution, and highlight the promise of applying
the approaches and methodologies of synthetic and medical chemistry
in the pursuit of synthetic biology.
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Affiliation(s)
- Aaron W. Feldman
- Department of Chemistry, The Scripps Research Institute, La
Jolla, California 92037, United States
| | - Floyd E. Romesberg
- Department of Chemistry, The Scripps Research Institute, La
Jolla, California 92037, United States
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5
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Feldman AW, Fischer EC, Ledbetter MP, Liao JY, Chaput JC, Romesberg FE. A Tool for the Import of Natural and Unnatural Nucleoside Triphosphates into Bacteria. J Am Chem Soc 2018; 140:1447-1454. [PMID: 29338214 DOI: 10.1021/jacs.7b11404] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Nucleoside triphosphates play a central role in biology, but efforts to study these roles have proven difficult because the levels of triphosphates are tightly regulated in a cell and because individual triphosphates can be difficult to label or modify. In addition, many synthetic biology efforts are focused on the development of unnatural nucleoside triphosphates that perform specific functions in the cellular environment. In general, both of these efforts would be facilitated by a general means to directly introduce desired triphosphates into cells. Previously, we demonstrated that recombinant expression of a nucleoside triphosphate transporter from Phaeodactylum tricornutum (PtNTT2) in Escherichia coli functions to import triphosphates that are added to the media. Here, to explore the generality and utility of this approach, we report a structure-activity relationship study of PtNTT2. Using a conventional competitive uptake inhibition assay, we characterize the effects of nucleobase, sugar, and triphosphate modification, and then develop an LC-MS/MS assay to directly measure the effects of the modifications on import. Lastly, we use the transporter to import radiolabeled or 2'-fluoro-modified triphosphates and quantify their incorporation into DNA and RNA. The results demonstrate the general utility of the PtNTT2-mediated import of natural or modified nucleoside triphosphates for different molecular or synthetic biology applications.
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Affiliation(s)
- Aaron W Feldman
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Emil C Fischer
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Michael P Ledbetter
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Jen-Yu Liao
- Department of Pharmaceutical Sciences, University of California , Irvine, California 92697, United States
| | - John C Chaput
- Department of Pharmaceutical Sciences, University of California , Irvine, California 92697, United States
| | - Floyd E Romesberg
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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6
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Zhang Y, Ptacin JL, Fischer EC, Aerni HR, Caffaro CE, San Jose K, Feldman AW, Turner CR, Romesberg FE. A semi-synthetic organism that stores and retrieves increased genetic information. Nature 2017; 551:644-647. [PMID: 29189780 PMCID: PMC5796663 DOI: 10.1038/nature24659] [Citation(s) in RCA: 215] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 10/20/2017] [Indexed: 02/08/2023]
Abstract
Since at least the last common ancestor of all life on Earth, genetic information has been stored in a four-letter alphabet that is propagated and retrieved by the formation of two base pairs. The central goal of synthetic biology is to create new life forms and functions, and the most general route to this goal is the creation of semi-synthetic organisms whose DNA harbours two additional letters that form a third, unnatural base pair. Previous efforts to generate such semi-synthetic organisms culminated in the creation of a strain of Escherichia coli that, by virtue of a nucleoside triphosphate transporter from Phaeodactylum tricornutum, imports the requisite unnatural triphosphates from its medium and then uses them to replicate a plasmid containing the unnatural base pair dNaM-dTPT3. Although the semi-synthetic organism stores increased information when compared to natural organisms, retrieval of the information requires in vivo transcription of the unnatural base pair into mRNA and tRNA, aminoacylation of the tRNA with a non-canonical amino acid, and efficient participation of the unnatural base pair in decoding at the ribosome. Here we report the in vivo transcription of DNA containing dNaM and dTPT3 into mRNAs with two different unnatural codons and tRNAs with cognate unnatural anticodons, and their efficient decoding at the ribosome to direct the site-specific incorporation of natural or non-canonical amino acids into superfolder green fluorescent protein. The results demonstrate that interactions other than hydrogen bonding can contribute to every step of information storage and retrieval. The resulting semi-synthetic organism both encodes and retrieves increased information and should serve as a platform for the creation of new life forms and functions.
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Affiliation(s)
- Yorke Zhang
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, USA
| | | | - Emil C Fischer
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, USA
| | | | | | | | - Aaron W Feldman
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, USA
| | | | - Floyd E Romesberg
- Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, USA
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7
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Abstract
To bestow cells with novel forms and functions, the goal of synthetic biology, we have developed the unnatural nucleoside triphosphates dNaMTP and dTPT3TP, which form an unnatural base pair (UBP) and expand the genetic alphabet. While the UBP may be retained in the DNA of a living cell, its retention is sequence-dependent. We now report a steady-state kinetic characterization of the rate with which the Klenow fragment of E. coli DNA polymerase I synthesizes the UBP and its mispairs in a variety of sequence contexts. Correct UBP synthesis is as efficient as for a natural base pair, except in one sequence context, and in vitro performance is correlated with in vivo performance. The data elucidate the determinants of efficient UBP synthesis, show that the dNaM-dTPT3 UBP is the first generally recognized natural-like base pair, and importantly, demonstrate that dNaMTP and dTPT3TP are well optimized and standardized parts for the expansion of the genetic alphabet.
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Affiliation(s)
- Sydney E. Morris
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Aaron W. Feldman
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Floyd E. Romesberg
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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8
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Feldman AW, Romesberg FE. In Vivo Structure-Activity Relationships and Optimization of an Unnatural Base Pair for Replication in a Semi-Synthetic Organism. J Am Chem Soc 2017; 139:11427-11433. [PMID: 28796508 DOI: 10.1021/jacs.7b03540] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In an effort to expand the genetic alphabet and create semi-synthetic organisms (SSOs) that store and retrieve increased information, we have developed the unnatural base pairs (UBPs) dNaM and d5SICS or dTPT3 (dNaM-d5SICS and dNaM-dTPT3). The UBPs form based on hydrophobic and packing forces, as opposed to complementary hydrogen bonding, and while they are both retained within the in vivo environment of an Escherichia coli SSO, their development was based on structure-activity relationship (SAR) data generated in vitro. To address the likely possibility of different requirements of the in vivo environment, we screened 135 candidate UBPs for optimal performance in the SSO. Interestingly, we find that in vivo SARs differ from those collected in vitro, and most importantly, we identify four UBPs whose retention in the DNA of the SSO is higher than that of dNaM-dTPT3, which was previously the most promising UBP identified. The identification of these four UBPs further demonstrates that when optimized, hydrophobic and packing forces may be used to replace the complementary hydrogen bonding used by natural pairs and represents a significant advance in our continuing efforts to develop SSOs that store and retrieve more information than natural organisms.
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Affiliation(s)
- Aaron W Feldman
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Floyd E Romesberg
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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9
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Feldman AW, Dien VT, Romesberg FE. Chemical Stabilization of Unnatural Nucleotide Triphosphates for the in Vivo Expansion of the Genetic Alphabet. J Am Chem Soc 2017; 139:2464-2467. [PMID: 28170246 DOI: 10.1021/jacs.6b12731] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We have developed an unnatural base pair (UBP) and a semisynthetic organism (SSO) that imports the constituent unnatural nucleoside triphosphates and uses them to replicate DNA containing the UBP. However, propagation of the UBP is at least in part limited by the stability of the unnatural triphosphates, which are degraded by cellular and secreted phosphatases. To circumvent this problem, we now report the synthesis and evaluation of unnatural triphosphates with their β,γ-bridging oxygen replaced with a difluoromethylene moiety, yielding dNaMTPCF2 and dTPT3TPCF2. We find that although dNaMTPCF2 cannot support in vivo replication, likely due to poor polymerase recognition, dTPT3TPCF2 can, and moreover, its increased stability can contribute to increased UBP retention. The data demonstrate the promise of this chemical approach to SSO optimization, and suggest that other modifications should be sought that confer phosphatase resistance without interfering with polymerase recognition.
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Affiliation(s)
- Aaron W Feldman
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Vivian T Dien
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Floyd E Romesberg
- Department of Chemistry, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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10
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Feldman AW, Ovaska SI, Ovaska TV. Facile Access to Cyclooctanoid Ring Systems via Microwave-Assisted Tandem 6-exo dig Cyclization-Rearrangement Sequence. Tetrahedron 2014; 70:4147-4155. [PMID: 24994941 DOI: 10.1016/j.tet.2014.02.089] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Appropriately substituted 5-alkyn-1-ol systems bearing a nitrile moiety at the triple bond serve as versatile precursors to a variety of cyclooctenone derivatives via a "one-pot" base-catalyzed oxyanionic 6-exo dig cyclization/Claisen rearrangement sequence under microwave irradiation. It was found that the initially formed cyclic intermediate consists of a mixture of endo and exocyclic isomers, which appear to be in equilibrium under the reaction conditions. However, the only observed products from these reactions are α-cyano substituted cyclooctenones, derived from the exocyclic dihydrofuran intermediates.
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Affiliation(s)
- Aaron W Feldman
- Department of Chemistry, Connecticut College, 270 Mohegan Avenue, New London, Connecticut 06320, United States of America
| | - Sami I Ovaska
- Department of Chemistry, Connecticut College, 270 Mohegan Avenue, New London, Connecticut 06320, United States of America
| | - Timo V Ovaska
- Department of Chemistry, Connecticut College, 270 Mohegan Avenue, New London, Connecticut 06320, United States of America
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11
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Liptak GS, Keller BB, Feldman AW, Chamberlin RW. Enhancing infant development and parent-practitioner interaction with the Brazelton Neonatal Assessment Scale. Pediatrics 1983; 72:71-8. [PMID: 6866594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Studies performed in low socioeconomic populations have shown that the demonstration of a newborn's developmental capacity to his mother during the first few days post partum enhances subsequent mother-infant interactions. This study was undertaken to determine whether demonstrating the Brazelton Neonatal Assessment Scale to white middle-class mothers would result in similar outcomes. Mothers of 75 neonates were randomly assigned to either an experimental group or to one of two control groups. Direct observation, subjective assessment of mother-infant interactions, and maternal questionnaires were used 1 and 3 months later to assess outcomes on several dimensions. Mothers in the experimental group spent more time playing with, talking to, and looking at their infants than did those in either control group, and were less likely to use feeding as a method of interacting with their infants. Experimental group mothers also were more likely to ask developmentally related questions. However, no differences were found in most indices of maternal-infant interaction used. The results of this study and a review of the literature indicate that the recommendation that such a demonstration be performed with all neonates must be weighed against the other methods available for enhancing infant development and healthy parent-child interaction.
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12
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Gardner JM, Feldman AW, Zablotowicz RM. Identity and Behavior of Xylem-Residing Bacteria in Rough Lemon Roots of Florida Citrus Trees. Appl Environ Microbiol 1982; 43:1335-42. [PMID: 16346030 PMCID: PMC244237 DOI: 10.1128/aem.43.6.1335-1342.1982] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
An aseptic vacuum extraction technique was used to obtain xylem fluid from the roots of rough lemon (
Citrus jambhiri
Lush.) rootstock of Florida citrus trees. Bacteria were consistently isolated from vascular fluid of both healthy and young tree decline-affected trees. Thirteen genera of bacteria were found, the most frequently occurring genera being
Pseudomonas
(40%),
Enterobacter
(18%),
Bacillus, Corynebacterium
, and other gram-positive bacteria (16%), and
Serratia
(6%). Xylem bacterial counts fluctuated seasonally. Bacterial populations ranged from 0.1 to 22 per mm
3
of root tissue (about 10
2
to 2 × 10
4
bacteria per g of xylem) when bacterial counts were made on vascular fluid, but these numbers were 10- to 1,000-fold greater when aseptically homogenized xylem tissue was examined similarly. Some of the resident bacteria (4%) are potentially phytopathogenic. It is proposed that xylem bacteria have an important role in the physiology of citrus.
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Affiliation(s)
- J M Gardner
- Institute of Food and Agricultural Sciences, Agricultural Research and Education Center, University of Florida, Lake Alfred, Florida 33850
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