2 research outputs found
Elucidation of Gephyronic Acid Biosynthetic Pathway Revealed Unexpected SAM-Dependent Methylations
Gephyronic acid, a cytostatic polyketide
produced by the myxobacterium <i>Cystobacter violaceus</i> Cb vi76, exhibits potent and selective eukaryotic protein synthesis
inhibition. Next-generation sequencing of the <i>C. violaceus</i> genome revealed five type I polyketide synthases and post-PKS tailoring
enzymes including an <i>O</i>-methyltransferase and a cytochrome
P450 monooxygenase. Seven methyltransferase (MT) domains embedded
within the PKS subunits were found to install the methyl branches
throughout the gephyronic acid skeleton. A rare loading domain from
the GNAT superfamily also contains an embedded MT domain that catalyzes
the in situ production of an isobutyryl starter unit. Phylogenetic
analysis identified new motifs that distinguish MT domains located
in PKS pathways with <i>in cis</i> acyltransferase (AT)
domains from MT domains located in PKS pathways with <i>trans</i> AT enzymes. The identification of the gene cluster sets the stage
for the generation of a heterologous expression system, which will
allow further investigation of selective eukaryotic protein synthesis
inhibitors through the generation of gephyronic acid analogues
Hollow Cathode Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride Using Pentachlorodisilane
In
this work, a novel chlorodisilane precursor, pentachlorodisilane
(PCDS, HSi<sub>2</sub>Cl<sub>5</sub>), was investigated for the growth
of silicon nitride (SiN<sub><i>x</i></sub>) via hollow cathode
plasma-enhanced atomic layer deposition (PEALD). A well-defined self-limiting
growth behavior was successfully demonstrated over the growth temperature
range of 270–360 °C. At identical process conditions,
PCDS not only demonstrated approximately >20% higher growth per
cycle
than that of a commercially available chlorodisilane precursor, hexachlorodisilane
(Si<sub>2</sub>Cl<sub>6</sub>), but also delivered a better or at
least comparable film quality determined by characterizing the refractive
index, wet etch rate, and density of the films. The composition of
the SiN<sub><i>x</i></sub> films grown at 360 °C using
PCDS, as determined by X-ray photoelectron spectroscopy, showed low
O content (∼2 at. %) and Cl content (<1 at. %; below the
detection limit). Fourier transform infrared spectroscopy spectra
suggested that N–H bonds were the dominant hydrogen-containing
bonds in the SiN<sub><i>x</i></sub> films without a significant
amount of Si–H bonds originating from the precursor molecules.
The possible surface reaction pathways of the PEALD SiN<sub><i>x</i></sub> using PCDS on the surface terminated with amine
groups (−NH<sub>2</sub> and −NH−) are proposed.
The PEALD SiN<sub><i>x</i></sub> films grown using PCDS
also exhibited a leakage current density as low as 1–2 nA/cm<sup>2</sup> at 2 MV/cm and a breakdown electric field as high as ∼12
MV/cm