dictyNews
Electronic Edition
Volume 44, number 17
June 29, 2018
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Abstracts
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Convergent evolution of integration site selection upstream of
tRNA genes by yeast and amoeba retrotransposons
Eva Kling, Thomas Spaller, Jana Schiefner, Doreen Bönisch,
Thomas Winckler
Pharmaceutical Biology, Institute of Pharmacy, Friedrich Schiller
University Jena, Germany
Nucleic Acids Research, accepted
Transposable elements amplify in genomes as selfish DNA
elements and challenge host fitness because their intrinsic
integration steps during mobilization can compromise genome
integrity. In gene-dense genomes, transposable elements are
notably under selection to avoid insertional mutagenesis of host
protein-coding genes. We describe an example of convergent
evolution in the distantly related amoebozoan Dictyostelium
discoideum and the yeast Saccharomyces cerevisiae, in which
the D. discoideum retrotransposon DGLT-A and the yeast Ty3
element developed different mechanisms to facilitate position-
specific integration at similar sites upstream of tRNA genes.
Transcription of tRNA genes by RNA polymerase III requires the
transcription factor complexes TFIIIB and TFIIIC. Whereas Ty3
recognizes tRNA genes mainly through interactions of its
integrase with TFIIIB subunits, the DGLT-A-encoded ribonuclease
H contacts TFIIIC subunit Tfc4 at an interface that covers
tetratricopeptide repeats (TPRs) 7 and 8. A major function of this
interface is to connect TFIIIC subcomplexes tauA and tauB and
to facilitate TFIIIB assembly. During the initiation of tRNA gene
transcription tauB is displaced from tauA, which transiently
exposes the TPR 7/8 surface of Tfc4 on tauA. We propose that
the DGLT-A intasome uses this binding site to obtain access to
genomic DNA for integration during tRNA gene transcription.
submitted by: Thomas Winckler [[log in to unmask]]
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Microfluidic single-cell analysis of oxidative stress in Dictyostelium
discoideum
Kathy Rodogiannis, Jessica T. Duong, and Michelle L. Kovarik
Analyst, accepted
Microfluidic chemical cytometry is a powerful technique for
examining chemical contents of individual cells, but applications
have focused on cells from multicellular organisms, especially
mammals. We demonstrate the first use of microfluidic chemical
cytometry to examine a unicellular organism, the social amoeba
Dictyostelium discoideum. We used the reactive oxygen species
indicator dichlorodihydrofluorescein diacetate to report on
oxidative stress and controlled for variations in indicator loading
and retention using carboxyfluorescein diacetate as an internal
standard. After optimizing indicator concentration, we investigated
the effect of peroxide treatment through single-cell measurements
of 353 individual cells. The peak area ratio of dichlorofluorescein
to carboxyfluorescein increased from 1.69 ± 0.89 for untreated
cells to 5.19 ± 2.72 for cells treated with 40 mM hydrogen peroxide.
Interestingly, the variance of the data also increased with oxidative
stress. While preliminary, these results are consistent with the
hypothesis that heterogeneous stress responses in unicellular
organisms may be adaptive.
submitted by: Michelle Kovarik [[log in to unmask]]
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[End dictyNews, volume 44, number 17]
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