Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers
Ming-Chang Chen, Christopher Mancuso, Carlos Hernández-García, Franklin Dollar, Ben Galloway, Dimitar Popmintchev, Pei-Chi Huang, Barry Walker, Luis Plaja, Agnieszka A. Jaroń-Becker, Andreas Becker, Margaret M. Murnane, Henry C. Kapteyn, and Tenio Popmintchev
Attosecond pulses driven by femtosecond lasers make it possible to capture the fastest electron dynamics in molecules and materials. To date, attosecond pulses driven by widely available 800-nm lasers were limited to the extreme UV region of the spectrum, which restricted the range of materials, liquid, and molecular systems that could be explored because of the limited penetrating power. Our recent work showed that longer-wavelength midinfrared driving lasers at wavelengths from 1 to 4 µm are optimal for generating shorter-wavelength, bright, soft X-ray beams. Here we show (pp. E2361–E2367) that longer-pulse-duration midinfrared lasers are also optimal for generating shorter-pulse-duration, attosecond, soft X-rays. This is an unexpected and beautiful convergence of physics: bright, soft X-ray high harmonics naturally emerge as isolated attosecond bursts.
Coliphage HK022 Nun protein inhibits RNA polymerase translocation
Christal L. Vitiello, Maria L. Kireeva, Lucyna Lubkowska, Mikhail Kashlev, and Max Gottesman
Gene expression can be regulated at the level of transcription elongation. Coliphage HK022 Nun protein suppresses coliphage λ development by inhibiting transcription elongation. We have determined the mechanism of Nun action in a purified in vitro transcription system. Nun blocks RNA polymerase (RNAP) lateral movement on the DNA template, thereby preventing translocation. Nun requires a 9- to 10-bp RNA–DNA hybrid and recognizes RNA or DNA sequences at the 5′ end of the hybrid. Suppression of lateral movement of RNAP represents a newly described (pp. E2368–E2375) regulatory mechanism.
Control of catalytic efficiency by a coevolving network of catalytic and noncatalytic residues
Thomas A. McMurrough, Russell J. Dickson, Stephanie M. F. Thibert, Gregory B. Gloor, and David R. Edgell
Maximizing structural and functional information from multiple sequence alignments is difficult for protein families that exhibit extreme sequence variation. We addressed this issue by identifying covarying positions within the sequence alignment to predict networks of coevolving amino acid residues in LAGLIDADG homing endonucleases, enzymes used for genome-engineering applications. Intriguingly, the predicted coevolving network with the highest score includes the active-site metal-binding residues and adjacent residues. We were able to modulate catalytic efficiency ∼100-fold by substitution of residues in the network. Our data show (pp. E2376–E2383) that the evolutionary trajectory and fitness landscape of LAGLIDADG active sites is constrained by a barrier of coevolving residues and imply that generating an optimal coevolving network is an important consideration when engineering these endonucleases.
Yolk-sac–derived macrophages regulate fetal testis vascularization and morphogenesis
Tony DeFalco, Indrashis Bhattacharya, Alyna V. Williams, Dustin M. Sams, and Blanche Capel
A main requisite for organogenesis is the integration of vascular networks, which not only deliver oxygen and nutrients but also serve instructive roles in organ patterning that determine how organs develop into their final structure and function in the adult. Our previous work showed that vascularization is essential to induce formation of the primitive cord structures that give rise to the seminiferous tubules of the adult testis. Here we show (pp. E2384–E2393) that fetal macrophages are required to remodel the vasculature and refine organ compartments during differentiation of the gonad. This study reveals an underappreciated and likely vital role for macrophages in fetal organogenesis that may be relevant to the development of many organs.
IκB kinase-induced interaction of TPL-2 kinase with 14-3-3 is essential for Toll-like receptor activation of ERK-1 and -2 MAP kinases
Abduelhakem Ben-Addi, Agnes Mambole-Dema, Christine Brender, Stephen R. Martin, Julia Janzen, Sven Kjaer, Stephen J. Smerdon, and Steven C. Ley
TPL-2 is a MEK-1/2 kinase that mediates Toll-like receptor activation of ERK-1/2 MAP kinases in macrophages and is critical for TNF induction during inflammation. TPL-2 activation of MEK-1/2 requires release from its associated inhibitor NF-κB1 p105, resulting from p105 proteolysis triggered by the IκB kinase (IKK) complex. Here (pp. E2394–E2403), we show that IKK phosphorylation of the TPL-2 C terminus induces 14-3-3 association with TPL-2, stimulating its MEK kinase activity, which is essential for TPL-2 activation of ERK-1/2. The 14-3-3 binding to TPL-2 is also indispensible for its induction of TNF, which is regulated independently of ERK-1/2 activation. The IKK complex, a key regulator of NF-κB transcription factors, therefore directly controls two key steps for TPL-2 activation in inflammatory responses.
PHLDA3 is a novel tumor suppressor of pancreatic neuroendocrine tumors
Rieko Ohki, Kozue Saito, Yu Chen, Tatsuya Kawase, Nobuyoshi Hiraoka, Raira Saigawa, Maiko Minegishi, Yukie Aita, Goichi Yanai, Hiroko Shimizu, Shinichi Yachida, Naoaki Sakata, Ryuichiro Doi, Tomoo Kosuge, Kazuaki Shimada, Benjamin Tycko, Toshihiko Tsukada, Yae Kanai, Shoichiro Sumi, Hideo Namiki, Yoichi Taya, Tatsuhiro Shibata, and Hitoshi Nakagama
Pancreatic neuroendocrine tumors (PanNETs) are a rare pathology, and molecular mechanisms underlying their development have not been well defined. This article (pp. E2404–E2413) shows that a two-hit inactivation of the PHLDA3 gene is required for PanNET development: methylation of the locus and loss of heterozygosity. PHLDA3 functions as a suppressor of PanNETs via repression of Akt activity and downstream Akt-regulated biological processes. In addition, the tumor-suppressing pathway mediated by MEN1, a well known suppressor of PanNETs, is dependent on the pathway mediated by PHLDA3, and inactivation of PHLDA3 and MEN1 cooperatively contribute to PanNET development. A novel PHLDA3-mediated pathway of tumor suppression that is important in the development of PanNETs is demonstrated, and the findings may contribute to personalized medicine of PanNET patients.
Ribosomal protein–Mdm2–p53 pathway coordinates nutrient stress with lipid metabolism by regulating MCD and promoting fatty acid oxidation
Yong Liu, Yizhou He, Aiwen Jin, Andrey P. Tikunov, Lishi Zhou, Laura A. Tollini, Patrick Leslie, Tae-Hyung Kim, Lei O. Li, Rosalind A. Coleman, Zhennan Gu, Yong Q. Chen, Jeffrey M. Macdonald, Lee M. Graves, and Yanping Zhang
Although progress has been made in the characterization of p53 in regulating metabolism, very little is known about the signaling pathways involved in this regulation in response to stress in vivo. Here we show (pp. E2414–E2422) that p53 controls hepatic fatty acid oxidation in mice in response to fasting. Disruption of ribosome protein (RP)-mouse double minute (Mdm)2 binding in Mdm2C305F mice results in fasting-induced hepatosteatosis. A full-dosage of p53 and an intact RP-Mdm2-p53 pathway are required for the induction of malonyl coA decarboxylase (MCD), a critical regulator of fatty acid oxidation. Thus, the RP-Mdm2-p53 pathway functions as a key regulator of hepatic lipid homeostasis in response to nutrient deprivation stress, a function that has implications in organismal survival and tumor suppression.
PipX, the coactivator of NtcA, is a global regulator in cyanobacteria
Javier Espinosa, Francisco Rodríguez-Mateos, Paloma Salinas, Val F. Lanza, Ray Dixon, Fernando de la Cruz, and Asuncion Contreras
PII, a signal transduction protein involved in nitrogen control in bacteria and plants, and NtcA, the transcriptional nitrogen regulator of cyanobacteria, can form complexes with PII interacting protein X (PipX). We demonstrate (pp. E2423–E2430) by a combination of genetic, transcriptomic, and multivariate analyses that PipX is involved in a much wider interaction network affecting nitrogen assimilation, translation, and photosynthesis. Two groups of genes differentially regulated by pipX provided further insights into the function of NtcA–PipX complexes and an improved definition of the consensus NtcA binding motif. The other four groups suggested the involvement of PipX in NtcA-independent regulatory pathways. Our results pave the way to uncover new regulatory interactions and mechanisms in the control of gene expression in cyanobacteria.
Regulation of photosystem I light harvesting by zeaxanthin
Matteo Ballottari, Marcelo J. P. Alcocer, Cosimo D’Andrea, Daniele Viola, Tae Kyu Ahn, Annamaria Petrozza, Dario Polli, Graham R. Fleming, Giulio Cerullo, and Roberto Bassi
Chloroplasts are particularly prone to photooxidative damage, and carotenoids play a key role in photoprotection. Under excess light conditions, plants accumulate a carotenoid, zeaxanthin, involved in multiple photoprotection events. Although the function of zeaxanthin in photosystem II (PSII) has been investigated thoroughly, its role in photosystem I (PSI) had not been identified. In this work we report a zeaxanthin-dependent regulation of PSI functional antenna size in Arabidopsis thaliana. We identified (pp. E2431–E2438) a zeaxanthin-dependent quenching process coupled to improved photostability of PSI, as measured in isolated complexes and leaves. We show that, similar to its action in PSII, zeaxanthin binding to components of PSI leads to the formation of carotenoid radical cations, quenching a fraction of the excitation energy absorbed.