Biology subjects

Murakami, K.

Publications and source records attributed to Murakami, K..

4 recordsLinked to original sources

bioRxiv2018

Structural basis of HEAT-kleisin interactions in the human condensin I subcomplex

ABSTRUCTCondensin I is a multi-protein complex that plays an essential role in mitotic chromosome assembly and segregation in eukaryotes. It is composed of five subunits: two SMC (SMC2 and SMC4), a kleisin (CAP-H) and two HEAT-repeat (CAP-D2 and -G) subunits. Although it has been shown that balancing acts of the two HEAT-repeat subunits enable this complex to support dynamic assembly of chromosomal axes in vertebrate cells, its underlying mechanisms remain poorly understood. Here, we report the crystal structure of a human condensin I subcomplex comprising hCAP-G and hCAP-H. hCAP-H binds to the concave surfaces of a harp-shaped HEAT repeat domain of hCAP-G. A physical interaction between hCAP-G and hCAP-H is indeed essential for mitotic chromosome assembly recapitulated in Xenopus egg cell-free extracts. Furthermore, this study reveals that the human CAP-G-H subcomplex has the ability to interact with not only a double-stranded DNA, but also a single-stranded DNA, implicating potential, functional divergence of the vertebrate condensin I complex in mitotic chromosome assembly.

cell biology↗

bioRxiv2018

An adipocyte light-Opsin 3 pathway regulates the circadian clock and energy balance.

Almost all life forms can detect and decode light information for adaptive advantage. Examples include the visual system, where photoreceptor signals are processed into virtual images, and the circadian system, where light entrains a physiological clock. Here we describe a pathway in mice that employs encephalopsin (OPN3, a 480 nm light responsive opsin) to mediate light responses in murine adipocytes. The adipocyte light-OPN3 pathway regulates neonatal growth in mice and is required for at least three important functions including (1) photoentrainment of a local circadian clock, (2) extracellular matrix deposition, and (3) regulation of mitochondrial content and the proportion of \"brite\" adipocytes. Furthermore, we show that the light-OPN3 pathway is required for normal levels of uncoupling protein 1 (UCP1) in white and brown adipose tissue. Consequently, neonatal Opn3 germ-line and adipocyte-conditional null mice show a reduced ability to maintain their body temperature under cold stress. This was also observed in wild-type mice deprived of blue light. We hypothesize that the adipocyte light-OPN3 pathway provides a dynamically responsive, circadian clock-integrated mechanism for regulating adipocyte function and in turn directing metabolism to thermogenesis rather than anabolism. These data indicate an important role for peripheral light sensing in mammals and may have broad implications for human health given the unnatural lighting conditions in which we live.

physiology↗

bioRxiv2018

Cryo-EM structure of Escherichia coli σ70 RNAP and promoter DNA complex revealed a role of σ nonconserved region during the open complex formation

First step of gene expression is transcribing the genetic information stored in DNA to RNA by the transcription machinery including RNA polymerase (RNAP). In Escherichia coli, a primary {sigma}70 factor form the RNAP holoenzyme to express housekeeping genes. The {sigma}70 contains a large insertion at between the conserved regions 1.2 and 2.1, the {sigma} non-conserved region ({sigma}NCR), but its function remains to be elucidated. In this study, we determined the cryo-EM structures of the E. coli RNAP {sigma}70 holoenzyme and its complex with promoter DNA (open complex, RPo) at 4.2 and 5.75 [A] resolutions, respectively, to reveal native conformations of RNAP and DNA. The RPo structure presented here found an interaction between R157 residue in the {sigma}NCR and promoter DNA just upstream of the -10 element, which was not observed in a previously determined E. coli RNAP transcription initiation complex (RPo plus short RNA) structure by X-ray crystallography due to restraint of crystal packing effect. Disruption of the {sigma}NCR and DNA interaction by the amino acid substitution (R157E) influences the DNA opening around the transcription start site and therefore decreases the transcription activity of RNAP. We propose that the {sigma}NCR and DNA interaction is conserved in proteobacteria and RNAP in other bacteria replace its role with a transcription factor.

molecular biology↗

bioRxiv2017

Allosteric effector ppGpp potentiates the inhibition of transcript initiation by DksA

DksA and ppGpp are the central players in the Escherichia coli stringent response and mediate a complete reprogramming of the transcriptome from one optimized for rapid growth to one adapted for survival during nutrient limitation. A major component of the response is a reduction in ribosome synthesis, which is accomplished by the synergistic action of DksA and ppGpp bound to RNA polymerase (RNAP) inhibiting transcription of rRNAs. Here, we report the X-ray crystal structures of E. coli RNAP holoenzyme in complex with DksA alone and with ppGpp. The structures show that DksA accesses the template strand at the active site and the downstream DNA binding site of RNAP simultaneously and reveal that binding of the allosteric effector ppGpp reshapes the RNAP-DksA complex. The structural data support a model for transcriptional inhibition in which ppGpp potentiates the destabilization of open complexes on rRNA promoters by DksA. We also determined the structure of RNAP-TraR complex, which reveals the mechanism of ppGpp-independent transcription inhibition by TraR. This work establishes new ground for understanding the pleiotropic effects of DksA and ppGpp on transcriptional regulation in proteobacteria.\n\nHighlightsO_LIDksA has two modes of binding to RNA polymerase\nC_LIO_LIDksA is capable of inhibiting the catalysis and influences the DNA binding of RNAP\nC_LIO_LIppGpp acts as an allosteric effector of DksA function\nC_LIO_LIppGpp stabilizes DksA in a more functionally important binding mode\nC_LI

molecular biology↗