Extracellular visfatin activates gluconeogenesis in HepG2 cells through the classical PKA/CREB-dependent pathway

Adipokines reportedly affect hepatic gluconeogenesis, and the adipokine visfatin is known to be related to insulin resistance and type 2 diabetes. However, whether visfatin contributes to hepatic gluconeogenesis remains unclear. Visfatin, also known as nicotinamide phosphoribosyltransferase (NAMPT), modulates sirtuin1 (SIRT1) through the regulation of nicotinamide adenine dinucleotide (NAD). Therefore, we investigated the effect of extracellular visfatin on glucose production in HepG2 cells, and evaluated whether extracellular visfatin affects hepatic gluconeogenesis via an NAD+-SIRT1-dependent pathway. Treatment with visfatin significantly increased glucose production and the mRNA expression and protein levels of phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) in HepG2 cells in a time- and concentration-dependent manner. Knockdown of SIRT1 had no remarkable effect on the induction of gluconeogenesis by visfatin. Subsequently, we evaluated if extracellular visfatin stimulates the production of gluconeogenic enzymes through the classical protein kinase A (PKA)/cyclic AMP-responsive element (CRE)-binding protein (CREB)-dependent process. The phosphorylation of CREB and PKA increased significantly in HepG2 cells treated with visfatin. Additionally, knockdown of CREB and PKA inhibited visfatin-induced gluconeogenesis in HepG2 cells. In summary, extracellular visfatin modulates glucose production in HepG2 cells through the PKA/CREB pathway, rather than via SIRT1 signaling.

Photochemically crosslinked collagen annulus plug: a potential solution solving the leakage problem of cell-based therapies for disc degeneration

Intra-disc injection of mesenchymal stem cells (MSCs) to treat disc degeneration may lead to unfavorable complications, particularly osteophyte formation. Development of an effective method to block the injection portal, prevent the leakage of injected cells and materials and, hence, prevent osteophyte formation is of the utmost importance before MSC-based therapies can be applied in a clinical setting. Here we seek to alleviate the cell leakage problem and the associated complication osteophyte formation by developing an injectable annulus plug to block the injection portal during intra-disc delivery. Specifically, we fabricated a needle-shaped collagen plug by photochemical crosslinking and successfully delivered it intra-discally, in association with MSCs in collagen microsphere carriers, using a custom-made delivery device. The mechanical performance of the plug and its effectiveness in reducing cell leakage were evaluated ex vivo under compression and in torsion push-out tests. The results demonstrate that the plug survived physiologically relevant loadings and significantly reduced leakage and enhanced retention of the injected materials. Finally, a pilot in vivo study in rabbits was conducted to evaluate the performance of the plug. Microcomputed tomography imaging and histology revealed that the plug significantly reduced osteophyte formation. This work suggests the potential of the annulus plug as an adjunct or annulus closure device for intra-disc delivery of cells and materials.

Isolation and characterization of 20 polymorphic microsatellite markers for Juglans mandshurica (Juglandaceae)

PREMISE OF THE STUDY

Fifty microsatellite loci were developed for the endangered species Juglans mandshurica to investigate its genetic diversity and population structure. •

METHODS AND RESULTS

In all, 50 microsatellite markers were isolated from J. mandshurica, using the Fast Isolation by AFLP of Sequences COntaining repeats (FIASCO) protocol. Twenty of these polymorphic markers were assessed in samples collected from 98 individuals among five populations in northeastern China. Across all of the J. mandshurica samples, the number of alleles per locus ranged from one to 17. •

CONCLUSIONS

These new microsatellite loci will be useful for conservation genetics studies of J. mandshurica.

[Effects of precipitation variation on the distribution pattern of soil fungal diversity in broad-leaved Korean pine mixed forest]

Broad-leaved Korean pine mixed forest is a kind of zonal climax vegetation with ecological significance in Northeast China, whereas Changbai Mountain is an ideal area to study the effects of precipitation variation on temperate forest. Taking the virgin broad-leaved Korean pine mixed forest in Changbai Mountain as the object, and based on T-RFLP method, this paper analyzed the spatial heterogeneity of fungal diversity in 0-5 cm and 5-10 cm soil layers and in rhizosphere soil at three different precipitation plots (30% increase, 30% decrease, and the control). Both the increase and the decrease of precipitation increased the diversity of soil fungi, but the dominant population changed. In 0-5 cm and 5-10 cm soil layers, the T-RFs over 500 bp increased with precipitation; in rhizosphere soil, the T-RFs responded to precipitation variation were 380 bp, 455 bp, and 487 bp, and the response mode was more complicated than that in surface soil layers. The results of CCA showed that the fungal community composition was significantly affected by soil pH, organic carbon, total nitrogen, and organic phosphorus.

Development and characterization of polymorphic microsatellite loci in Phellodendron amurense (Rutaceae)

PREMISE OF THE STUDY

Microsatellite markers were developed for the rare species Phellodendron amurense to assess the genetic diversity and population structure of this plant. •

METHODS AND RESULTS

In total, 27 microsatellite markers were developed for P. amurense by using an enriched genomic library and hybridization; all of these primers successfully amplified DNA fragments in P. amurense. These markers were screened in 74 individuals from four populations in China; 15 loci were found to be polymorphic, with the number of alleles per locus ranging from one to nine. •

CONCLUSIONS

The microsatellite markers developed here represent a useful tool for studying the population genetic structure of P. amurense and to inform toward the development of effective conservation programs for this species.

Needle-age related variability in nitrogen, mobile carbohydrates, and δ13C within Pinus koraiensis tree crowns

For both ecologists and physiologists, foliar physioecology as a function of spatially and temporally variable environmental factors such as sunlight exposure within a tree crown is important for understanding whole tree physiology and for predicting ecosystem carbon balance and productivity. Hence, we studied concentrations of nitrogen (N), non-structural carbohydrates (NSC = soluble sugars + starch), and δ(13)C in different-aged needles within Pinus koraiensis tree crowns, to understand the needle age- and crown position-related physiology, in order to test the hypothesis that concentrations of N, NSC, and δ(13)C are needle-age and crown position dependent (more light, more photosynthesis affecting N, NSC, and δ(13)C), and to develop an accurate sampling strategy. The present study indicated that the 1-yr-old needles had significantly higher concentration levels of mobile carbohydrates (both on a mass and an area basis) and N(area) (on an area basis), as well as NSC-N ratios, but significantly lower levels of N(mass) (on a mass basis) concentration and specific leaf area (SLA), compared to the current-year needles. Azimuthal (south-facing vs. north-facing crown side) effects were found to be significant on starch [both on a mass (ST(mass)) and an area basis (ST(area))], δ(13)C values, and N(area), with higher levels in needles on the S-facing crown side than the N-facing crown side. Needle N(mass) concentrations significantly decreased but needle ST(mass), ST(area), and δ(13)C values significantly increased with increasing vertical crown levels. Our results suggest that the sun-exposed crown position related to photosynthetic activity and water availability affects starch accumulation and carbon isotope discrimination. Needle age associated with physiological activity plays an important role in determining carbon and nitrogen physiology. The present study indicates that across-scale sampling needs to carefully select tissue samples with equal age from a comparable crown position.

[Characteristics of terrestrial ecosystem primary productivity in East Asia based on remote sensing and process-based model]

Based on the bi-linearly interpolated meteorological reanalysis data from National Centers for Environmental Prediction, USA and by using the leaf area index data derived from the GIMMS NDVI to run the process-based Boreal Ecosystems Productivity Simulator (BEPS) model, this paper simulated and analyzed the spatiotemporal characteristics of the terrestrial ecosystem gross primary productivity (GPP) and net primary productivity (NPP) in East Asia in 2000-2005. Before regional simulating and calculating, the observation GPP data of different terrestrial ecosystem in 15 experimental stations of AsiaFlux network and the inventory measurements of NPP at 1300 sampling sites were applied to validate the BEPS GPP and NPP. The results showed that BEPS could well simulate the changes in GPP and NPP of different terrestrial ecosystems, with the R2 ranging from 0.86 to 0.99 and the root mean square error (RMSE) from 0.2 to 1.2 g C x m(-2) x d(-1). The simulated values by BEPS could explain 78% of the changes in annual NPP, and the RMSE was 118 g C x m(-2) x a(-1). In 2000-2005, the averaged total GPP and total NPP of the terrestrial ecosystems in East Asia were 21.7 and 10.5 Pg C x a(-1), respectively, and the GPP and NPP exhibited similar spatial and temporal variation patterns. During the six years, the total NPP of the terrestrial ecosystems varied from 10.2 to 10.7 Pg C x a(-1), with a coefficient of variation being 2. 2%. High NPP (above 1000 g C x m(-2) x a(-1)) occurred in the southeast island countries, while low NPP (below 30 g C x m(-2) x a(-1)) occurred in the desert area of Northwest China. The spatial patterns of NPP were mainly attributed to the differences in the climatic variables across East Asia. The NPP per capita also varied greatly among different countries, which was the highest (70217 kg C x a(-1)) in Mongolia, far higher than that (1921 kg C x a(-1)) in China, and the lowest (757 kg C x a(-1)) in India.

[Radiometers performance attenuation and data correction in long-term observation of total radiation and photosynthetically active radiation in typical forest ecosystems in China]

Based on the total radiation and photosynthetically active radiation (PAR) observations with net radiometer (CNR1) and quantum sensor (Li-190SB) in 4 ChinaFLUX forest sites (Changbaishan, Qianyanzhou, Dinghushan, and Xishuangbanna) in 2003-2008, this paper analyzed the uncertainties and the radiometers performance changes in long-term and continuous field observation. The results showed that the 98% accuracy of the total radiation measured with CNR1 (Q(cNR1)) could satisfy the technical criterion for the sites except Xishuangbanna where the Q(CNR1) was averagely about 7% lower than Q(CM11), the radiation measured with high accuracy pyranometer CM11. For most sites, though the temperature had definite effects on the performance of CNR1, the effects were still within the allowable range of the accuracy of the instrument. Besides temperature, the seasonal fog often occurred in tropical rain forests in Xishuangbanna also had effects on the performance of CNR1. Based on the long-term variations of PAR, especially its ratio to total radiation in the 4 sites, it was found that quantum sensor (Li-190SB) had obvious performance attenuation, with the mean annual attenuation rate being about 4%. To correct the observation error caused by Li-190SB, an attempt was made to give a post-correction of the PAR observations, which could basically eliminate the quantum sensor's performance attenuation due to long-term field measurement.

Does Near-Infrared Spectroscopy Provide an Early Warning of Low Haematocrit following the Initiation of Hypothermic Cardiopulmonary Bypass in Cardiac Surgery?

This study investigated 151 patients undergoing cardiac surgery to determine whether measurement of regional cerebral oxygen saturation (rScO2) using near-infrared spectroscopy (NIRS) can indicate a low haematocrit after initiation of hypothermic cardiopulmonary bypass (CPB). Haematocrit, rScO2, haemoglobin level, arterial partial pressures of carbon dioxide and oxygen, systemic blood pressure, and nasopharyngeal and rectal temperatures were determined 5 min after the initial administration of heparin for CPB and 90 s after completion of the first cardioplegic solution injection. Immediately after initiation of hypothermic CPB, rScO2, haemoglobin and haematocrit values were significantly lower than those before CPB. No significant correlations were found between the change in haematocrit and changes in left, right and mean rScO2; thus, changes in rScO2 before and after initiation of hypothermic CPB did not reflect changes in haematocrit values. This indicates that NIRS cannot provide early warning of a low haematocrit immediately after initiation of hypothermic CPB in cardiac surgery.

Identification of 11 novel mutations in 49 Korean patients with mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) or Hunter syndrome is a rare lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase (IDS). As MPS II is X-linked, patients are usually males with heterogeneous mutations ranging from point mutations to gross deletions and recombination. In 2003, we reported a mutation analysis of 25 patients with MPS II. In this study, 31 mutations in another 49 Korean patients (45 families) with MPS II are reported: 12 missense, nine deletions, four splicing, two nonsense, two insertions, one deletion/insertion, and IDS-IDS2 recombination mutations. Among these mutations, 11 were novel ones (4 missense mutations: Ser61Pro, Pro97Arg, Pro228Ala, and Pro261Ala; 5 deletions: c.344delA, c.420delG, c.768delT, c.1112delC and c.1402delC; 1 deletion/insertion: c.1222delinsTA; and 1 insertion mutation: c.359_360insATCC). The IDS-IDS2 recombination mutations were most frequently observed; all patients with this mutation had the severe MPS II phenotype. However, most of the patients (5/7) with the G374G splicing mutation had an attenuated phenotype, except for two sibling cases with the severe phenotype. Except for a few recurrent mutations such as the G374G, R443X, L522P, and recombination mutations, each patient had a unique individual mutation. Therefore, careful interpretation of genotype-phenotype correlations is warranted.

[Clinical results of posterolateral fusion in treating lumbar low-grade spondylolisthesis]

OBJECTIVE

To analyze the clinical outcomes and losses of correction for posterolateral fusion on low-grade lumbar spondylolisthesis.

METHODS

From October 2001 to July 2008, 37 patients with a mean age of 60.1 years (range, 27 - 88 years) with low-grade lumbar spondylolisthesis treated with posterolateral fusion, including 9 males and 28 females, were reviewed retrospectively. The clinical outcomes were evaluated using the visual analogue scale (VAS) and Oswestry disability index (ODI). The fusion status and loss of correction were assessed using plain radiographs and CT.

RESULTS

All the 37 patients had got complete follow-up for 14 - 96 months (average 36.4 months); post-operative reduction rate was 76.4%, and 34 patients (91.9%) showed loss of correction with a mean loss rate 5.8% (range, -3.0% - 25.8%). The percentage of slip of pre-operative, post-operative and final follow-up indicated significant difference (P < 0.05)compared with each other; post-operative intervertebral disc height indicated significant difference in comparison with that of pre-operatively and at final follow-up (P < 0.05); lumbar lordosis angle at final follow-up showed significant difference when compared with that of pre-operatively and postoperatively (P < 0.05); VAS and ODI at final follow-up indicated significant difference in contrast to that of pre-operative (P < 0.05). Upon final follow-up, the complications were found in 2 cases who presented degenerative scoliosis at 15 and 17 months after the surgery, in 1 case with cranial adjacent segment retrolisthesis at the 14 months after the surgery, in 1 case with cut-out and breakage of screws at the 24 months after the surgery, and in 1 case with postoperative infection which were cured after debridement.

CONCLUSIONS

For mid-term follow-up of low-grade lumbar spondylolisthesis, posterolateral fusion shows loss of correction in most cases, but presents good clinical outcome and fusion rate.

[Woody plant fine root biomass and its spatial distribution in top soil of broad-leaved Korean pine forest in Changbai Mountain]

Geostatistic method was applied to study the spatial distribution of woody plant fine root biomass in a natural broad-leaved Korean pine (Pinus koraiensis) mixed forest soil in Changbai Mountain. The investigation was carried out in three selected plots, sized 50 m x 50 m, in 2008. In the three plots, the living fine root biomass in surface soil (0-20 cm) was 3.195, 1.930, and 2.085 t x hm(-2), and the dead fine root biomass was 0.971 0.581, and 0.790 t x hm(-2), respectively. In 0-10 cm soil layer, the living fine root biomass had no correlation with the dead fine root biomass; but in 10-20 cm soil layer, a significant positive correlation was found between them (r = 0.352, P < 0.05). The variograms of living fine root biomass and dead fine root biomass could be well fitted by spherical model. Spatial variation explained more than 70% of the total variance of fine root biomass across three plots. The regressed ranges were 5.2, 14. 6, and 9.8 m for living fine root biomass, and 4.3, 20.4, and 20.1 m for dead fine root biomass in plots 1, 2, and 3, respectively. For comparison, Bayesian method was also used to estimate the ranges for the fine root biomass. The results obtained by geostatistic method and Bayesian method were consistent with each other.

Comparison of eddy covariance and chamber-based methods for measuring CO2 flux in a temperate mixed forest

Two methods, eddy covariance and chamber-based measurements, were employed to measure the net ecosystem CO(2) exchange in a mature temperate mixed forest in 2003. The eddy covariance system was used as a reference, which was compared with the chamber-based method. Based on chamber fluxes, the ecosystem had a gross primary production of 1490 g C m(-2) year(-1), 90% of which was released as efflux back into the air via respiration of the entire ecosystem. This was comprised of about 48% from soil surface CO(2) efflux, 31% from leaf respiration and 21% from stem and branch respiration. Net ecosystem exchange (NEE), estimated from the sum of daily component fluxes, was 146 g C m(-2) year(-1). Ecosystem respiration (ER), estimated from the sum of daily ecosystem respiration, was 1240 g C m(-2) year(-1). NEE was 9.8% of actual gross primary production (GPP). The eddy covariance estimates of NEE, ER and GPP were 188, 1030 and 1220 g C m(-2) year(-1), respectively. The eddy covariance estimation of NEE was higher than that of the chamber-based estimation by 22.5%. On a daily basis, NEE of the scaled chamber measurements was in acceptable agreement with eddy covariance measurement data with R(2) values of 0.71. The discrepancy between the measurement of the two methods was greater in the non-growing season primarily due to the lack of spatial variability in the scaled chamber estimates and weak atmosphere turbulence by eddy covariance measurements. There are many uncertainties for determination of absolute values of ecosystem component flux. More detailed experiments and related theoretical studies are needed in the future.

[Carbon dynamics of broad-leaved Korean pine forest ecosystem in Changbai Mountains and its responses to climate change]

By using process model Sim-CYCLE based on dry matter production theory, this paper estimated the gross primary productivity (GPP), net primary productivity (NPP), net ecosystem productivity (NEP), ecosystem carbon storage (WE), total plant carbon storage (WP), and total soil carbon storage (WS) of broad-leaved Korean pine forest ecosystem in Changbai Mountains from 1982 to 2003, and analyzed the variations of these indices under present climate condition and carbon equilibrium state as well as the responses of these indices to climate change scenarios in the future. Under present climate condition, the estimated GPP, NPP, and NEP were 14.9, 8.7, and 2.7 Mg C x hm(-2) x a(-1), being 2.8 Mg C x hm(-2) x a(-1) less and 1.4 and 0.2 Mg C x hm(-2) x a(-1) higher than the measured values, respectively. The NEP in June-August occupied more than 90% of the annual NEP, and the maximum monthly NEP appeared in July (1.23 Mg C x hm(-2) month(-1)). The estimated WE, WP, and WS were 550.8, 183.8, and 367.0 Mg C x hm(-2), respectively, very close to the measured values. From present climate condition to carbon equilibrium state, the estimated carbon storages of the forest ecosystem increased to some extent, with the GPP and NPP being 17.7 and 7.3 Mg C x hm(-2) x a(-1), respectively, suggesting that the role of the forest ecosystem as a carbon "sink" declined gradually with the increase of carbon storage. A 2 degree C-increment of air temperature did not benefit the increase of GPP, NPP and NEP, while doubling CO2 concentration was in adverse. The effects of the combination of doubling CO2 concentration and 2 degree C-increment of air temperature on the GPP, NPP, and NEP were similar to those of doubling CO2 concentration. The climate change scenario in the future had the same effects both on the carbon storage and on the productivity of the forest ecosystem, which was mainly correlated to the effects of primary productivity on the carbon storage.

Simulation on combined rapid gravity filtration and backwash models

Combined rapid gravity filtration and backwash models have been applied to simulate filtration and backwash cycles. The simulated results from the backwash model suggest that an optimum air flow rate exists to maximise particle removal efficiency in the backwash operation for a certain backwash system. The simulation of combined rapid gravity filtration and backwash models suggests that the filter should not be completely cleaned up in the backwash and a certain amount of particles retained on filter grains after backwash can be beneficial for subsequent filtration runs. This is consistent with the experimental results in the literature.

Simulation of combined rapid gravity filtration and backwash models

Combined rapid gravity filtration and backwash models are applied to simulate filtration and backwash cycles. The simulated results from the backwash model suggest that air flow rate can be optimised to maximise particle removal efficiency in the backwash for a particular system. The simulation of combined rapid gravity filtration and backwash models suggests that efficient backwash operation is essential for maintaining the life time of a filter. However, the filter is not advised to be completely cleaned up in the backwash and the particles retained on filter grains after the backwash can be beneficial for subsequent filtration runs.

[Decomposition of litter organic matter and its relations to C, N and P release in secondary conifer and broadleaf mixed forest in Changbai Mountains]

By using litterbag method, the decomposition processes of 9 types of foliar litter in secondary conifer and broadleaf mixed forest in Changbai Mountains were assessed during a period of 34 months. The initial N and P concentrations varied greatly among the litters, and there were significant relationships between litter decomposition constant (k) and initial N concentration and C/N. The percent organic matter remaining had a significant linear correlation with percent C remaining, and a significant polynomial correlation with percent N and P remaining. The percent N and P remaining increased with the decomposition of organic matter in its initial decomposition phase, but decreased gradually in the latter decomposition phase. C/N and C/P declined with the decrease of percent organic matter remaining, and the differences in C/N or C/P among litter types decreased, being approached to 23 and 350, respectively by the end of the study. During organic matter decomposition, N/P did not change greatly, and the differences in N/P between litter types declined when the percent organic matter remaining was below 25%. Our study showed that percent of C, N and P mass remaining can be predicted by percent of organic matter mass remaining.

[Simulation of crown leaf area index of Korean pine and broadleaved mixed forest in Chang-Bai mountains]

Based on the 3-year successive automatic measurement of photosynthetic active radiation above and under the crown of Korean pine and broadleaved mixed forest in Changbai Mountains, as well as the seasonal observation on leaf area index, a semi-empirical model was established to estimate the crown leaf area index of the forest. The results showed that this model could well reflect the seasonal variation of crown leaf area. From the comparison of 3-year leaf area index series, it was found that the date when the leaf area index began to rise was postponed if the date when its air temperature stably surpassed 0 degrees C came late. The dynamics of the leaf area index in whole growth season could be divided into three stages, i. e., rising, relatively stable, and dropping, and at each stage, there was a greater correlation between the leaf area index and the accumulated temperature above 0 degrees C, which could be expressed by Logistic curve and linear equation. The problems existing in the observation and estimation of forest crown leaf area index were discussed.

Monte Carlo simulation of the photon beam characteristics from medical linear accelerators

The MCNPX code has been employed on a personal computer to calculate the dosimetric characteristics of the photon beams from the 6 MV Siemens MX2 and the 10 MV Varian Clinac 2100C linear accelerators. A model of the treatment head includes the major geometric structure within the beam path. The model was used to calculate the energy spectra of the photon beam, percentage depth dose and the dose profiles. The accuracy of the calculated results is examined by comparing them with the measured dose distributions for the two machines. The computed and measured depth dose curves agree to within 2% for all the depths beyond the build-up region for both treatment machines. The calculations agree to within 2% of the measured profiles within the 100-50% dose level. It has been found that the MCNPX code is an effective tool for simulating the clinical photon beam.

The development of fetal surgery

The history of fetal surgery features an absolute dependency upon the possibility of diagnosis before birth. Powerful new imaging methods, the techniques of sampling amniotic fluid and fetal tissue, and modern molecular genetics for the prenatal diagnosis of various congenital diseases have removed the veil of secrecy from the fetus. Even though most prenatally detected congenital malformations can be managed after maternal transport, a few simple anatomic defects require fetal surgery, albeit with predictably poor results. The understanding of intrauterine physiology and pathophysiology in several congenital malformations has been worked out in animal model study, and the natural history of congenital defects revealed by prenatal observations on human fetuses. Selection criteria for intrauterine intervention have been developed. Over the last two decades, surgical techniques for open and endoscopic fetal surgery have been defined and anesthesia and tocolysis for fetal surgery improved. As we enter the 21st century, this field of surgery will surely expand.

The structural and functional organization of the yeast mediator complex

The Mediator complex of Saccharomyces cerevisiae is required for diverse aspects of transcription by RNA polymerase II (pol II). Mediator is composed of two functionally distinct subcomplexes, Rgr1 and Srb4. To identify the structures and functions of each subcomplex, we expressed recombinant proteins for each subunit and assayed their interactions with each other and with basal transcription proteins. The Rgr1 subcomplex is composed of the Gal11 module, which binds activators, and the Med9/10 module. The Med9/10 module is required for both transcriptional activation and repression, and these activities appear to be carried out by two submodules. Proteins in the Med9 submodule interact physically and genetically with Srb10/11, suggesting that the Med9 submodule mediates the repression of pol II. Purified recombinant Srb4 subcomplex stimulated basal transcription of pol II but had little effect on activated transcription and phosphorylation of the C-terminal domain of the Rpb1 subunit of pol II. Both subcomplexes of Mediator interacted with a distinct set of basal transcription factors and pol II. The modular organization of Mediator and the associated functions suggest that the Mediator complex may recruit and/or stabilize the preinitiation complex through several points of contact with transcriptional regulators and basal transcription factors.

Med9/Cse2 and Gal11 modules are required for transcriptional repression of distinct group of genes

The yeast Mediator is composed of two subcomplexes, Rgr1 and Srb4, known to be required for diverse aspects of transcriptional regulation; however, their structural and functional organizations have not yet been deciphered in detail. Biochemical analyses designed to determine the subunit composition of the Rgr1 subcomplex revealed that the regulator-interacting subcomplex has a modular structure and is composed of the Gal11, Med9/Cse2, and Med10/Nut2 modules. Genome-wide gene expression and Northern analyses performed in the presence or absence of the various Mediator modules revealed a distinct requirement for the Gal11, Med9/Cse2, and Med10/Nut2 modules in transcriptional repression as well as activation. GST pull-down analysis revealed that the transcriptional repressor Tup1 binds to distinct but overlapping regions of the Gal11 module that were shown previously to be transcriptional activator binding sites. These data suggest that competition between transcriptional activators and repressors for a common binding site in the Mediator and distinct conformational changes in the Mediator induced by repressor binding may underlie the mechanism of transcriptional repression in eukaryotes.