Adhesion of endothelial cells using self-assembly peptides under precise deformation control of tissue-engineered vessels

The objective of this study was to anchor endothelial cells using self-assembly peptides under precise deformation control of tissue-engineered vessels. An acelluarized vascular matrix was used as the control group to examine the function of self-assembly peptides. In the experiment group, the self-assembly peptides were added to the inner surface of tissue-engineered vessels to form a monolayer. Then the endothelial cells were injected into the vascular lumen. A deformation control system was developed which was based on real-time image analysis and feedback control system. After dynamic culture by different deformation (set points 1, 5, and 10 per cent), the endothelial cell densities of experimental and control groups were compared. Both the self-assembly peptides and the extent of deformation affected the endothelial cell density on the inner surface of tissue-engineered vessels. The construct with self-assembly peptides under 5 per cent deformation gained the highest endothelial cell density. It was concluded that the deformation of assembled peptides contributes to the development and adhesion of endothelial cells in the inner surface of tissue-engineered vessels.

The p73 polymorphisms are not associated with susceptibility to esophageal squamous cell carcinoma in a high incidence region of China

P73, a p53 homolog, has some p53-like activities and plays an important role in modulating cell cycle, apoptosis and DNA repair. The two linked polymorphisms in the non-coding region of exon2 of p73 gene, named G4C14-A4T14, may alter translation efficiency of the gene. The transcription of p73 gene is initiated by three promoters, termed P1-P3. There is a single nucleotide substitution (-386G/A) in the P3 promoter region with unknown function. To test the hypothesis that the genetic variations in the exon2 and P3 promoter play a role in the etiology of esophageal squamous cell carcinoma (ESCC), we conducted a population-based case-control study in 348 ESCC patients and 583 healthy controls from a high incidence region of Hebei province, China. The p73 polymorphisms were genotyped by polymerase chain reaction-restriction fragment length polymorphism analysis (PCR-RFLP). The results showed that the family history of upper gastrointestinal cancer (UGIC) significantly increased the risk of developing ESCC (the age, sex and smoking status adjusted OR = 2.02, 95% CI = 1.54-2.67). The overall distribution of the p73 genotype, allelotype and haplotype in cancer patients and controls were not significantly different (all P-values are above 0.05). Stratification analysis by smoking status and family history of UGIC also did not show the significant influence of the polymorphisms on the risk of ESCC development. The results suggested that the p73 exon2 G4C14-A4T14 and P3 promoter -386G/A polymorphisms might not be used as potential markers to predicate the risk of ESCC development in northern China.

A model system for increasing the intensity of whole-cell biocatalysis: investigation of the rate of oxidation of D-sorbitol to L-sorbose by thin bi-layer latex coatings of non-growing Gluconobacter oxydans

We developed a novel <50-microm thick nano-porous bi-layer latex coating for preserving Gluconobacter oxydans, a strict aerobe, as a whole cell biocatalyst. G. oxydans was entrapped in an acrylate/vinyl acetate co-polymer matrix (T (g) approximately 10 degrees C) and cast into 12.7-mm diameter patch coatings (cellcoat) containing approximately 10(9) CFU covered by a nano-porous topcoat. The oxidation of D-sorbitol to L-sorbose was used to investigate the coating catalytic properties. Intrinsic kinetics was studied in microbioreactors using a pH 6.0 D-sorbitol, phosphate, pyruvate (SPP) non-growth medium at 30 degrees C, and the Michaelis-Menten constants determined. By using a diffusion cell, cellcoat and topcoat diffusivities, optimized by arresting polymer particle coalescence by glycerol and/or sucrose addition, were determined. Cryo-FESEM images revealed a two-layer structure with G. oxydans surrounded by <40-nm pores. Viable cell density, cell leakage, and oxidation kinetics in SPP medium for >150 h were investigated. Even though the coatings were optimized for permeability, approximately 50% of G. oxydans viability was lost during cellcoat drying and further reduction was observed as the topcoat was added. High reaction rates per unit volume of coating (80-100 g/L x h) were observed which agreed with predictions of a diffusion-reaction model using parameters estimated by independent experiments. Cellcoat effectiveness factors of 0.22-0.49 were observed which are 20-fold greater than any previously reported for this G. oxydans oxidation. These nano-structured coatings and the possibility of improving their ability to preserve G. oxydans viability may be useful for engineering highly reactive adhesive coatings for multi-phase micro-channel and membrane bioreactors to dramatically increase the intensity of whole-cell oxidations.

Decision support for tendon tissue engineering

The aim of this study is to provide decision support with artificial intelligence for tendon tissue engineering strategies. The experimental data of tissue-engineered tendons were integrated and standardized with a centralized database, and a decision support system was developed using both artificial neural networks and decision trees. The decision support system was trained with existing cases in the database, and then was used to generate tissue engineering schemes for new experimental animals. Following the schemes generated by the artificial intelligent system, we cured 28 of the 30 experimental animals. In conclusion, artificial intelligence is a powerful method for decision support in the tendon tissue engineering realm.

Gender-specific proteomic alterations in glycolytic and mitochondrial pathways in aging monkey hearts

We utilized proteomic techniques in a primate model (Macaca fascicularis) of aging to determine potential mechanisms to explain gender differences in protection of the aging heart. The majority of prior work in this field utilized rodent models, and importantly no prior study utilized a proteomic approach in the aging heart. We studied changes in proteins in seven monkeys in each group (young and old males and females (YMs, OMs, YFs, and OFs, respectively)), and used two-dimensional gel electrophoresis in combination with mass spectrometry in five monkeys in each group. We found decreases (P < 0.05) in the expression of key enzymes in glycolysis (e.g. pyruvate kinase, alpha-enolase, triosephosphate isomerase), glucose oxidation (e.g. pyruvate dehydrogenase E1 beta-subunit), and the tricarboxylic acid (TCA) cycle (2-oxoglutarate dehydrogenase) in left ventricular (LV) samples from OM monkeys; these changes in glycolytic, glucose oxidation, and TCA enzymes were not observed either in YMs, YFs or OFs. We found additional gender differences in the reduced expression and function of proteins that are responsible for electron transport and oxidative phosphorylation in mitochondria only in hearts from OM monkeys, with corresponding decreased oxidation rates with NADH and ascorbate-N,N,N',N' ''-tetramethyl-p-phenylenediamine substrates. The changes in glycolytic and mitochondrial metabolic pathways in OM monkey hearts are similar to changes observed in hearts affected by diabetes or LV dysfunction, and could be involved in the mechanism for the cardiomyopathy of aging. The sparing of these changes in OF hearts could be involved in the mechanism mediating delayed cardiovascular risk in OFs.

Hzf-3 expression in the amygdala after establishment of conditioned taste aversion

We studied the regulation of the expression of the inducible orphan nuclear receptor known as HZF-3 (or Nurr1) in acquisition of conditioned taste aversion in rats. Our results show that HZF-3 expression in the lateral/basolateral (LA/BLA) amygdala complex was significantly up-regulated when both the conditioned and the unconditioned stimuli were paired, but not when either of the stimuli was presented alone. Induction in the LA/BLA had a faster onset than induction in the central nucleus of the amygdala. The results implicate HZF-3 in the acquisition of associative aversive experiences.

The dynamics of bone marrow stromal cells in the proliferation of multipotent hematopoietic progenitors by substance P: an understanding of the effects of a neurotransmitter on the differentiating hematopoietic stem cell

Communication within the hematopoietic-neuroendocrine-immune axis is partly mediated by neurotransmitters (e.g. substance P, SP) and cytokines. SP mediates neuromodulation partly through the stimulation of bone marrow (BM) progenitors. This study shows that SP, through the neurokinin-1 receptor, stimulates the proliferation of primitive hematopoietic progenitors: cobblestone-forming cells (CAFC, CD34+). This effect is optimal when macrophage is included within the fibroblast support. Indirect induction of IL-1 could be important in the proliferation of CAFC colonies by SP. Phenotypic and functional studies suggest that SP might directly interact with the CD34+/CD45(dim) population. These studies indicate that SP can initiate a cascade of biological responses in the BM stroma and stem cells to stimulate hematopoiesis.

Correlation between transcriptome and interactome mapping data from Saccharomyces cerevisiae

Genomic and proteomic approaches can provide hypotheses concerning function for the large number of genes predicted from genome sequences. Because of the artificial nature of the assays, however, the information from these high-throughput approaches should be considered with caution. Although it is possible that more meaningful hypotheses could be formulated by integrating the data from various functional genomic and proteomic projects, it has yet to be seen to what extent the data can be correlated and how such integration can be achieved. We developed a 'transcriptome-interactome correlation mapping' strategy to compare the interactions between proteins encoded by genes that belong to common expression-profiling clusters with those between proteins encoded by genes that belong to different clusters. Using this strategy with currently available data sets for Saccharomyces cerevisiae, we provide the first global evidence that genes with similar expression profiles are more likely to encode interacting proteins. We show how this correlation between transcriptome and interactome data can be used to improve the quality of hypotheses based on the information from both approaches. The strategy described here may help to integrate other functional genomic and proteomic data, both in yeast and in higher organisms.

Identification of potential interaction networks using sequence-based searches for conserved protein-protein interactions or "interologs"

Protein interaction maps have provided insight into the relationships among the predicted proteins of model organisms for which a genome sequence is available. These maps have been useful in generating potential interaction networks, which have confirmed the existence of known complexes and pathways and have suggested the existence of new complexes and or crosstalk between previously unlinked pathways. However, the generation of such maps is costly and labor intensive. Here, we investigate the extent to which a protein interaction map generated in one species can be used to predict interactions in another species.

TFIIH inhibits CDK9 phosphorylation during human immunodeficiency virus type 1 transcription

Tat stimulates human immunodeficiency virus, type 1 (HIV-1), transcription elongation by recruitment of the human transcription elongation factor P-TEFb, consisting of CDK9 and cyclin T1, to the TAR RNA structure. It has been demonstrated further that CDK9 phosphorylation is required for high affinity binding of Tat/P-TEFb to the TAR RNA structure and that the state of P-TEFb phosphorylation may regulate Tat transactivation. We now demonstrate that CDK9 phosphorylation is uniquely regulated in the HIV-1 preinitiation and elongation complexes. The presence of TFIIH in the HIV-1 preinitiation complex inhibits CDK9 phosphorylation. As TFIIH is released from the elongation complex between +14 and +36, CDK9 phosphorylation is observed. In contrast to the activity in the "soluble" complex, phosphorylation of CDK9 is increased by the presence of Tat in the transcription complexes. Consistent with these observations, we have demonstrated that purified TFIIH directly inhibits CDK9 autophosphorylation. By using recombinant TFIIH subcomplexes, our results suggest that the XPB subunit of TFIIH is responsible for this inhibition of CDK9 phosphorylation. Interestingly, our results further suggest that the phosphorylated form of CDK9 is the active kinase for RNA polymerase II carboxyl-terminal domain phosphorylation.

Defective interplay of activators and repressors with TFIH in xeroderma pigmentosum

Inherited mutations of the TFIIH helicase subunits xeroderma pigmentosum (XP) B or XPD yield overlapping DNA repair and transcription syndromes. The high risk of cancer in these patients is not fully explained by the repair defect. The transcription defect is subtle and has proven more difficult to evaluate. Here, XPB and XPD mutations are shown to block transcription activation by the FUSE Binding Protein (FBP), a regulator of c-myc expression, and repression by the FBP Interacting Repressor (FIR). Through TFIIH, FBP facilitates transcription until promoter escape, whereas after initiation, FIR uses TFIIH to delay promoter escape. Mutations in TFIIH that impair regulation by FBP and FIR affect proper regulation of c-myc expression and have implications in the development of malignancy.

Active remodeling of somatic nuclei in egg cytoplasm by the nucleosomal ATPase ISWI

Cloning by the transplantation of somatic nuclei into unfertilized eggs requires a dramatic remodeling of chromosomal architecture. Many proteins are specifically lost from nuclei, and others are taken up from the egg cytoplasm. Recreating this exchange in vitro, we identified the chromatin-remodeling nucleosomal adenosine triphosphatase (ATPase) ISWI as a key molecule in this process. ISWI actively erases the TATA binding protein from association with the nuclear matrix. Defining the biochemistry of global nuclear remodeling may facilitate the efficiency of cloning and other dedifferentiation events that establish new stem cell lineages.

Rapid assay of A1c-type glycosylated hemoglobin in blood of diabetic rats using fast protein liquid chromatography

AIM

To develop a fast protein liquid chromatography (FPLC) method for the assay of Alc-type glycosylated hemoglobin in diabetic rats.

METHODS

Venous blood was collected from rats. After the erythrocytes were washed and sedimented, the hemolysate was prepared and diluted with isotonic saline as a sample for the assay. Samples were then separated on Mono_S_HR_5/5 cation exchange column by a lithium chloride gradient elution system. The Alc-type glycosylated hemoglobin was monitored by measuring the absorbance at 415 nm.

RESULTS

The Alc-type glycosylated hemoglobin was well separated from total hemoglobin. The average HbAlc amount in diabetic rats was determined to be (3.6% +/- 0.6%, n = 7), while the corresponding figure in normal rats was (1.4% +/- 0.4%, n = 7, P < 0.01).

CONCLUSION

This FPLC method is easy, rapid and reproducible, and can be used for an assay of diabetic rat HbAlc to evaluate and screen new drugs for diabetes mellitus therapy.

Regional hyperthermia in the treatment of primary hepatic carcinoma

BACKGROUND AND OBJECTIVES

The purpose of this research was to investigate the clinical significance of regional hyperthermia in the treatment of primary hepatic carcinoma (PHC).

METHODS

The regional hyperthermia (60 degrees C) was used whenever there was suspicion of residual cancer tissues on the edge of the hepatic resection. The hyperthermia was maintained for about 5-20 min depending on the size and the amounts of residual nodulus. If there was obvious necrosis on the hyperthermia-treated site, the solidified tissues were removed. Otherwise, the solidified tissues were kept in situ.

RESULTS

There were 68 cases of PHC patients in this study. The patients were divided into 4 groups: A, lobectomy, 14 cases; B, lobectomy plus regional hyperthermia, 12 cases; C, regional hepatectomy, 16 cases; D, regional hepatectomy plus regional hyperthermia, 26 cases. All patients were followed after their operations. The mean survival time of the 4 groups was as follows: Group A, 346.5 days (186-921 days); Group B, 432.6 days (254-1189 days); Group C, 525.4 days (192-1016 days); and Group D, 1142 (from 318 days to seven years and two months) days. There were significant differences between Groups A and B (P < 0.01) and between Groups C and D (P < 0.01). It seems that regional hyperthermia on the hepatic resection edge can prolong patients' survival time.

CONCLUSIONS

Regional hyperthermia on the hepatic resection edge is helpful for prolonging patients' survival time in the treatment of primary hepatic carcinoma.

Analysis of mouse fertilin in wild-type and fertilin beta(-/-) sperm: evidence for C-terminal modification, alpha/beta dimerization, and lack of essential role of fertilin alpha in sperm-egg fusion

The sperm surface protein fertilin functions in sperm-egg interaction. On guinea pig and bovine sperm, fertilin is a heterodimer of alpha and beta subunits. Both subunits are initially synthesized as precursors and then proteolytically processed by removing N-terminal domains. Since the mouse is currently the main mammalian species in which fertilization is studied, in the present report, we analyzed the structure, processing, and expression of fertilin in mouse. We found that the processing of mouse fertilin beta occurs during epididymal maturation and involves changes in the cytoplasmic tail domain as well as the N-terminal domains. Although we (R. Yuan et al., 1997, J. Cell Biol. 137, 105-112) and others (M. S. Chen et al., 1999, J. Cell Biol. 144, 549-561) have previously reported that mature fertilin beta is 55-57 kDa, here we show that 55 kDa is an unrelated protein in the sperm extract which cross-reacts with an antibody that recognizes precursor, but not mature, fertilin beta. Comparison of Western blots of wild-type and fertilin beta knockout sperm revealed that authentic, mature fertilin beta is 45 kDa. We also obtained direct evidence that mouse fertilin alpha and beta exist as a heterodimer. In addition, we found that in mice lacking the fertilin beta subunit, fertilin alpha is absent from mature sperm. A widely proposed model for sperm-egg fusion suggests that fertilin alpha is the sperm component that promotes membrane fusion by undergoing a conformational change that exposes a virus-like, hydrophobic fusion peptide. Because sperm lacking fertilin alpha and fertilin beta can fuse with eggs at 50% the wild-type rate, this model is called into question. The results suggest instead that other gamete surface molecules act to promote membrane fusion and that fertilin's role in gamete fusion is in sperm-egg plasma membrane adhesion.

Autoantibodies to DFS 70 kd/transcription coactivator p75 in atopic dermatitis and other conditions

BACKGROUND

Sera of patients with atopic dermatitis (AD) were found to have autoantibodies that reacted with tissue culture cell substrates in immunohistochemistry to display a characteristic pattern of nuclear distribution of dense fine speckles. The sera also recognized a 70-kd protein on Western immunoblots, and the antigen was termed dense fine speckles 70 kd (DSF70).

OBJECTIVE

Because spontaneously occurring autoantibodies could be immune responses to proteins that might be participating in the disease process, it was of interest to identify the antigens driving the autoimmune antibody response.

METHODS

A serum containing high-titer antibodies to DFS70 was used to immunoscreen a complementary (c)DNA expression library to isolate cDNA encoding the antigen. After the cDNA was isolated, this was used to express recombinant protein to determine the prevalence of antibody in AD and other conditions.

RESULTS

Thirty percent of patients with AD were found to have antibody to recombinant DFS70 in Western immunoblots. Sixteen percent of patients with asthma and 9% of patients with interstitial cystitis had antibodies of the same specificities. The cDNA encoding DFS70 was identical to a transcription coactivator called p75, which had been shown to be required for RNA polymerase II-dependent transcription. Another important finding was that IgE antibodies to DFS70 were also present in AD sera.

CONCLUSION

It is suggested that a common basis for the presence of autoantibodies to DFS70 might be related to AD in asthma, interstitial cystitis, and other conditions. A possible role of this antigen-antibody system in pathogenesis remains to be demonstrated, but it appears to be a marker for a subset of patients with AD.

Phosphorylation of the RAP74 subunit of TFIIF correlates with Tat-activated transcription of the HIV-1 long terminal repeat

Transcription from the HIV-1 long terminal repeat (LTR) is regulated by the viral transactivator Tat, which increases RNA polymerase II (RNAP II) processivity. Previous reports have demonstrated that phosphorylation of the RNAP II carboxy-terminal domain by TFIIH and P-TEFb is important for Tat transactivation. Our present results demonstrate that phosphorylation of the RAP74 subunit of TFIIF is also an important step in Tat transactivation. Interestingly, while the general transcription factor TFIIF is required for both basal and Tat-activated transcription, phosphorylation of the RAP74 subunit occurs in the presence of Tat and correlates with a high level of transcription activity. Using a biotinylated DNA template transcription assay, we provide evidence that RAP74 is phosphorylated by TAF(II)250 during Tat-activated transcription. Depletion of RAP74 from the HeLa nuclear extract inhibited HIV-1 LTR-driven basal transcription and Tat transactivation. The addition of TFIIF, reconstituted from recombinant RAP30 and RAP74, to the depleted HeLa nuclear extract resulted in restoration of Tat transactivation. Of importance, the exogenous RAP74 was rapidly phosphorylated in the presence of Tat. These results suggest that RAP74 phosphorylation is one important step, of several, in the Tat transactivation cascade.

Human PC4 is a substrate-specific inhibitor of RNA polymerase II phosphorylation

The activity of cyclin-dependent protein kinases (cdks) is physiologically regulated by phosphorylation, association with the specific cyclin subunits, and repression by specific cdk inhibitors. All three physiological regulatory mechanisms are specific for one or more cdks, but none is known to be substrate specific. In contrast, synthetic cdk peptide inhibitors that specifically inhibit cdk phosphorylation of only some substrates, "aptamers," have been described. Here, we show that PC4, a naturally occurring transcriptional coactivator, competitively inhibits cdk-1, -2, and -7-mediated phosphorylation of the largest subunit of RNA polymerase II (RNAPII), but it does not inhibit phosphorylation of other substrates of the same kinases. Interestingly, the phosphorylated form of PC4 is devoid of kinase inhibitory activity. We also show that wild-type PC4 but not the kinase inhibitory-deficient mutant of PC4 represses transcription in vivo. Our results point to a novel role for PC4 as a specific inhibitor of RNAPII phosphorylation.

The FBP interacting repressor targets TFIIH to inhibit activated transcription

FUSE-binding protein (FBP) binds the single-stranded far upstream element of active c-myc genes, possesses potent transcription activation and repression domains, and is necessary for c-myc expression. A novel 60 kDa protein, the FBP interacting repressor (FIR), blocked activator-dependent, but not basal, transcription through TFIIH. Recruited through FBP's nucleic acid-binding domain, FIR formed a ternary complex with FBP and FUSE. FIR repressed a c-myc reporter via the FUSE. The amino terminus of FIR contained an activator-selective repression domain capable of acting in cis or even in trans in vivo and in vitro. The repression domain of FIR targeted only TFIIH's p89/XPB helicase, required at several stages in transcription, but not factors required for promoter selection. Thus, FIR locks TFIIH in an activation-resistant configuration that still supports basal transcription.

UPA, a universal protein array system for quantitative detection of protein-protein, protein-DNA, protein-RNA and protein-ligand interactions

Protein-protein interactions have been widely used to study gene expression pathways and may be considered as a new approach to drug discovery. Here I report the development of a universal protein array (UPA) system that provides a sensitive, quantitative, multi-purpose, effective and easy technology to determine not only specific protein-protein interactions, but also specific interactions of proteins with DNA, RNA, ligands and other small chemicals. (i) Since purified proteins are used, the results can be easily interpreted. (ii) UPA can be used multiple times for different targets, making it economically affordable for most laboratories, hospitals and biotechnology companies. (iii) Unlike DNA chips or DNA microarrays, no additional instrumentation is required. (iv) Since the UPA uses active proteins (without denaturation and renaturation), it is more sensitive compared with most existing methods. (v) Because the UPA can analyze hundreds (even thousands on a protein microarray) of proteins in a single experiment, it is a very effective method to screen proteins as drug targets in cancer and other human diseases.

Increased expression of intercellular adhesion molecule-1 in mouse focal cerebral ischemia model

OBJECTIVE

To quantitatively measure the temporal profiles of intercellular adhesion molecule-1 (ICAM-1) protein in mouse brain after middle cerebral artery occlusion (MCAO).

METHODS

Adult male CD-1 mice received 0, 3, 6, 12, 24, 48 and 72 hour(s) of permanent MCAO with an intraluminal suture technique. The degree and the extent of occlusion were determined using a laser Doppler flowmeter. ICAM-1 positive expression in ischemic regions was determined immunohistochemically and ICAM-1 protein was quantitatively measured using immunoprecipitation and Western blot analysis.

RESULTS

After MCAO, surface cerebral blood flow (CBF) in the ischemic hemisphere decreased to 9%-15% of the baseline in each time point of 7 to 8 animals. There were no significant differences in CBF measurement during occlusion between groups. Immunohistochemistry showed that ICAM-1 positive microvascular endothelial cells were observed both in the ischemic core and in the perifocal region. There was a tendency for increasing expression of ICAM-1 positive microvascular endothelial cells from the ischemic core to the ischemic margin. Western blot analysis showed that ICAM-1 expression in the ischemic hemisphere began to increase 3 h after MCAO, peaked at 6 h to 12 h, and persisted to 72 h.

CONCLUSIONS

ICAM-1 expression increases in mice with permanent MCAO because ICAM-1 can mediate leukocyte-endothelial adhesion and progression of leukocyte infiltration after permanent focal cerebral ischemia. ICAM-1 is one of the important factors participating in ischemic cerebral damage and pathogenesis of stroke.

Analysis of aberrant methylation of the VHL gene by transgenes, monochromosome transfer, and cell fusion

Several tumor suppressor genes were shown to be inactivated by a process involving aberrant de novo methylation of their GC-rich promoters which is usually associated with transcriptional repression. The mechanisms underlying this process are poorly understood. In particular this abnormal methylation may be caused and/or maintained by either deficiency of some trans-acting factor(s) or by various malfunctions acting in cis. Here we studied the nature of aberrant methylation of the von Hippel-Lindau (VHL) disease tumor suppressor gene in a human clear cell renal carcinoma cell line, UOK 121, that contains a silent hypermethylated endogenous VHL allele. First, we transfected unmethylated VHL transgenes, driven by the VHL promoter, into UOK 121 cells. Next, to exclude possible position effects that may influence methylation of the introduced VHL genes, we transferred a single chromosome 3, carrying an apparently normal hypomethylated VHL allele into the UOK 121 cells. Finally, we created somatic cell hybrids between UOK 121 and UMRC 6 cells containing a mutant VHL-expressing hypomethylated allele. In these three experiments both the methylation of the VHL promoter and the transcriptional status of the introduced and endogenous VHL alleles remained unchanged. Our results demonstrate that the putative trans-acting factors present in the UOK 121 and UMRC 6 cells are unable to induce changes in methylation pattern of the VHL alleles in all cell lines and hybrids studied. Taken together, the results indicate that cis-specific local features are pivotal in maintaining and perpetuating aberrant methylation of the VHL CpG island. Contribution of some putative trans-acting factors cannot be excluded during a period when the aberrant VHL methylation pattern was first generated.

The transcription factor Sp3 interacts with promoter elements of the lens specific MIP gene

PURPOSE

To characterize the cis regulatory elements and their interaction with transcription factors responsible for the lens specific expression of the MIP gene, which encodes the Major Intrinsic Protein of the lens fiber membranes.

METHODS

Study interaction of factors present in newborn mouse lens nuclear extracts with DNA fragments corresponding to mouse MIP gene 5' flanking sequence by electrophoresis mobility shift assay (EMSA) and DNase I footprinting.

RESULTS

We found a high degree of identity in the first 100 bp of 5' flanking sequence of mice and humans, however, a lower degree of conservation is observed further upstream. We have found by DNase I footprinting analysis that lens specific factors may interact with the first 100 bp of 5' flanking sequence. A domain containing an E box, conserved in mouse and human, may interact with a lens specific factor. However, general factors may interact with a NF-1 binding site. An overlapping GC and CT box is present in the mouse MIP gene. In the human MIP gene GC and CT boxes are found in different domains of the MIP gene promoter. Both CT boxes interact with factors present in lens nuclear extracts including Sp3. They are able to interact with purified Sp1but not with Sp1 present in mouse lens nuclear extracts.

CONCLUSIONS

The transcription factor Sp3 may play an important role in regulating MIP gene expression in the lens.

Interferon consensus sequence-binding protein is constitutively expressed and differentially regulated in the ocular lens

Interferon signaling is mediated by STATs and interferon regulatory factor (IRF) families of transcription factors. Ten distinct IRFs have been described and most are expressed in a variety of cells except for interferon consensus sequence-binding protein (ICSBP) and lymphoid-specific IRF/Pip that are thought to be exclusively expressed in lymphoid cells. We show here for the first time that ICSBP is constitutively and inducibly expressed in the mouse lens. In contrast to lymphoid cells with exclusive expression of ICSBP in the nucleus, ICSBP is present in both the cytoplasm and nucleus of the lens cell. However, ICSBP in the nucleus is of lower apparent molecular weight. We further show that the ICSBP promoter is constitutively bound by lens nuclear factors and that its activation requires binding of additional factors including STAT1. Furthermore, transcriptional activation of ICSBP gene by interferon gamma is accompanied by selective nuclear localization of ICSBP in proliferating epithelial cells but not in the nuclei of nondividing cells in the lens fiber compartment. Constitutive and inducible expression of ICSBP in the ocular lens and differential regulation of its subcellular localization in the developing lens suggest that ICSBP may have nonimmunity related functions and that the commonly held view that it is lymphoid-specific be modified.

A novel transcriptional coactivator, p52, functionally interacts with the essential splicing factor ASF/SF2

Increasing evidence suggests that pre-mRNA splicing can take place cotranscriptionally in vivo. However, insight into how these two processes are linked has been lacking. Here, we describe that a novel transcriptional coactivator, p52, interacts not only with transcriptional activators and general transcription factors to enhance activated transcription but also with the essential splicing factor ASF/SF2 both in vitro and in vivo to modulate ASF/SF2-mediated pre-mRNA splicing. Furthermore, immunofluorescence studies indicate that the majority of endogenous p52 is colocalized with ASF/SF2 in the nucleoplasm of HeLa cells. Together, these observations suggest that, in addition to functioning as a transcriptional coactivator, p52 may also act as an adaptor to coordinate pre-mRNA splicing and transcriptional activation of class II genes.

Isolation of cDNAs encoding novel transcription coactivators p52 and p75 reveals an alternate regulatory mechanism of transcriptional activation

Transcriptional activation in human cell-free systems containing RNA polymerase II and general initiation factors requires the action of one or more additional coactivators. Here, we report the isolation of cDNAs encoding two novel human transcriptional coactivators (p52 and p75) that are derived from alternatively spliced products of a single gene and share a region of 325 residues, but show distinct coactivator properties. p52 and p75 both show strong interactions with the VP16 activation domain and several components of the general transcriptional machinery. p52, like the previously described PC4, is a potent broad-specificity coactivator, whereas p75 is less active for most activation domains. These results suggest that p52 is a general transcriptional coactivator that mediates functional interactions between upstream sequence-specific activators and the general transcription apparatus, possibly through a novel mechanism.

Novel cofactors and TFIIA mediate functional core promoter selectivity by the human TAFII150-containing TFIID complex

TATA-binding protein-associated factors (TAFIIs) within TFIID control differential gene transcription through interactions with both activators and core promoter elements. In particular, TAFII150 contributes to initiator-dependent transcription through an unknown mechanism. Here, we address whether TAFIIs within TFIID are sufficient, in conjunction with highly purified general transcription factors (GTFs), for differential core promoter-dependent transcription by RNA polymerase II and whether additional cofactors are required. We identify the human homologue of Drosophila TAFII150 through cognate cDNA cloning and show that it is a tightly associated component of human TFIID. More importantly, we demonstrate that the human TAFII150-containing TFIID complex is not sufficient, in the context of all purified GTFs and RNA polymerase II, to mediate transcription synergism between TATA and initiator elements and initiator-directed transcription from a TAFII-dependent TATA-less promoter. Therefore, TAFII-promoter interactions are not sufficient for the productive core promoter-selective functions of TFIID. Consistent with this finding, we have partially purified novel cofactor activities (TICs) that potentiate the TAFII-mediated synergism between TATA and initiator elements (TIC-1) and TAFII-dependent transcription from TATA-less promoters (TIC-2 and -3). Furthermore, we demonstrate an essential function for TFIIA in TIC- and TAFII-dependent basal transcription from a TATA-less promoter. Our results reveal a parallel between the basal transcription activity of TAFIIs through core promoter elements and TAFII-dependent activator function.

p53 intron 2 genotypes detected in normal specimens and lung carcinomas in Hong Kong

Previous studies suggest that the polymorphic p53 intron 2 displays a high frequency of mutations, occurring with different frequencies in tumor tissues versus peripheral blood of lung cancer patients as compared to healthy individuals. We evaluated the significance of these polymorphisms and mutations utilizing matched triple specimens from the lung tumor, normal lung tissue, and peripheral blood of cancer patients. Identical genotypes were observed in normal tissues and blood, while 4 mutations were observed in tumors. The A1 allelic frequency was increased in the adenocarcinoma tissues as compared to normal tissues. Two p53 exon 2 polymorphisms were detected, appearing with equal frequencies among cancer patients and healthy individuals. The p53 intron 2 polymorphic locus is a hot spot for mutations in Hong Kong lung cancer patients.

Coactivation by OCA-B: definition of critical regions and synergism with general cofactors

Molecular dissection of the B-cell-specific transcription coactivator OCA-B has revealed distinct regions important, respectively, for recruitment to immunoglobulin promoters through interaction with octamer-bound Oct-1 and for subsequent coactivator function. Further analysis of general coactivator requirements showed that selective removal of PC4 from the essential USA fraction severely impairs Oct-1 and OCA-B function in a cell-free system reconstituted with partially purified factors. Full activity can be restored by the combined action of recombinant PC4 and the PC4-depleted USA fraction, thus suggesting a joint requirement for PC4 and another, USA-derived component(s) for optimal function of Oct-1/OCA-B in the reconstituted system. Indeed, USA-derived PC2 was found to act synergistically with PC4 in reproducing the function of intact USA in the assay system. Consistent with the requirement for PC4 in the reconstituted system, OCA-B was found to interact directly with PC4. Surprisingly, however, removal of PC4 from the unfractionated nuclear extract has no detrimental effect on OCA-B/Oct-1-dependent transcription. These results lead to a general model for the synergistic function of activation domains in Oct-1 and OCA-B (mediated by the combined action of the multiple USA components) and, further, suggest a functional redundancy in general coactivators.

Overlapping Sp1 and AP2 binding sites in a promoter element of the lens-specific MIP gene

The MIP gene, the founder of the MIP family of channel proteins, is specifically expressed in fiber cells of the ocular lens and expression is regulated temporally and spatially during development. We previously found that a DNA fragment containing 253 bp of 5'-flanking sequence and 42 bp of exon 1 of the human MIP gene contains regulatory elements responsible for lens-specific expression of the MIP gene. In this report we have analyzed the function of overlapping Sp1 and AP2 binding sites present in the MIP promoter. Using DNase I footprinting analysis we found that purified Sp1 and AP2 transcription factors interact with several domains of the human MIP promoter sequence -253/+42. Furthermore, addition of purified Sp1 to Drosophila nuclear extracts activates in vitro transcription from the MIP promoter -253/+42. This promoter activity is competed by oligonucleotides containing domains footprinted with Sp1. Using promoter-reporter gene ( CAT ) constructs we found that the sequence -39/-70 contains a cis regulatory element essential for promoter activity in transient assays in lens cells. EMSA analysis showed that lens nuclear extracts contain factors that bind to the MIP 5'-flanking sequence containing overlapping Sp1 and AP2 binding domains at positions -37/-65. Supershift experiments with lens nuclear extracts indicated that Sp3 is also able to interact with this regulatory element, suggesting that Sp1 and Sp3 may be involved in regulation of transcription of the MIP gene in the lens.

High-performance liquid chromatography of selenoamino acids and organo selenium compounds. Speciation by inductively coupled plasma mass spectrometry

As part of an ongoing study to identify selenium compounds with cancer chemopreventive activity, extracts of selenium-enriched samples were analyzed by HPLC-inductively coupled plasma (ICP)-MS. Ion-exchange, ion pair and derivatization methods for reversed-phase HPLC were considered and advantages and disadvantages for each compared. Anion exchange allows separation of selenite and selenate, but otherwise provides poor separation. Pre-column derivatization and reversed-phase chromatography provides separation of compounds with terminal amine functionalities, but many other species elute in the void volume. The ion pair method gave optimal separation and was compatible with standard ICP-MS operating conditions.

Acetylation of general transcription factors by histone acetyltransferases

The acetylation of histones increases the accessibility of nucleosomal DNA to transcription factors [1,2], relieving transcriptional repression [3] and correlating with the potential for transcriptional activity in vivo [4 - 7]. The characterization of several novel histone acetyltransferases - including the human GCN5 homolog PCAF (p300/CBP-associated factor) [8], the transcription coactivator p300/CBP [9], and TAFII250 [10] - has provided a potential explanation for the relationship between histone acetylation and transcriptional activation. In addition to histones, however, other components of the basal transcription machinery might be acetylated by these enzymes and directly affect transcription. Here, we examine the acetylation of the basal transcriptional machinery for RNA polymerase II by PCAF, p300 and TAFII250. We find that all three acetyltransferases can direct the acetylation of TFIIEbetaand TFIIF, and we identify a preferred site of acetylation in TFIIEbeta. Human TFIIE consists of two subunits, alpha(p56) and beta(p34), which form a heterotetramer (alpha2 beta2) in solution ([11], reviewed in [12]). TFIIE enters the preinitiation complex after RNA polymerase II and TFIIF, suggesting that TFIIE may interact directly with RNA polymerase II and/or TFIIF [13,14]. In addition, TFIIE can facilitate promoter melting either in the presence or absence of TFIIH and can stimulate TFIIH-dependent phosphorylation of the carboxy-terminal domain of RNA polymerase II [15-18]. TFIIF has an essential role in both transcription initiation and elongation ([19,20], for review see [21]). We discuss the implications of the acetylation of TFIIEbetaand TFIIF for transcriptional control by PCAF, p300 and TAFII250.

Analysis of L-myc and GSTM1 genotypes in Chinese non-small cell lung carcinoma patients

The genotypes of L-myc and GSTM1 genes were studied in normal lung tissues of 98 non-small cell lung carcinoma (NSCLC) patients from Hong Kong using polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) techniques. Results showed a statistical difference in L-myc genotypes between Chinese and African Americans (P = 0.02). A significant deficit in heterozygotes resulting in the departure from Hardy-Weinberg equilibrium in lung cancer female patients was detected (0.01 < P < 0.02). There were significant differences in survival times in patients having L-L and S-S genotypes, with shorter survival times in the patients with L-L genotypes (0.01 < P < 0.05). Data on age, size of tumor, histological types, and lymph node metastasis showed no significant association with L-myc genotype. The survival time in the GSTM1-negative (null gene) group was significantly different from the GSTM1 positive group between 16 and 24 months after operation (0.01 < P < 0.05). There was no significant difference in the distribution of GSTM1 genotypes between Chinese and Caucasian Americans.

Transcription-positive cofactor 4 forms complexes with HSSB (RPA) on single-stranded DNA and influences HSSB-dependent enzymatic synthesis of simian virus 40 DNA

The replication of simian virus 40 (SV40) DNA in vitro requires a trimeric single-stranded DNA (ssDNA)-binding protein called HSSB or RPA. HSSB supports the unwinding of DNA containing the SV40 origin in the presence of the viral-encoded T antigen and is required for the initiation of RNA primer synthesis as well as processive elongation of DNA catalyzed by the DNA polymerase delta holoenzyme. In this report we show that the transcription positive cofactor 4 (PC4), a ssDNA-binding protein, forms complexes with HSSB on ssDNA and markedly affects the replication functions of HSSB. PC4 supports T antigen-catalyzed unwinding of SV40 origins in lieu of HSSB but inhibits both RNA primer synthesis and polymerase delta-catalyzed DNA chain elongation reactions. These inhibitory effects can be reversed by the addition of excess HSSB. Depending on the concentration of HSSB, PC4 is capable of either inhibiting or activating SV40 DNA replication measured in both mono- and dipolymerase systems. The possible role of PC4 in the initiation of DNA replication is discussed.

[Human melanoma-specific peptide antigens recognized by HLA-A2 restricted tumor-infiltrating lymphocytes]

OBJECTIVE

HLA-A2-associated peptides were extracted from human melanoma cell lines and used to study human melanoma-specific peptide antigens for HLA-A2-restricted tumor-infiltrating lymphocyte (TIL).

METHODS

TILS were derived from the peripheral lymph nodes of HLA-A2+ human melanoma patients, HLA-A2 molecules were purified from the melanoma cell lines by immunoaffinity column chromatography of detergent-solubilized cell pellets. Peptides bound to the HLA-A2 molecules were acid eluted and fractionated by reversed phase RP-HPLC. Individual fractions were assessed for their ability to reconstitute melanoma-specific epitopes by adding to the HLA-A2+ Ag-processing mutant cell, T2.

RESULTS

These TIL lysed HLA-A2+ autologous and allogeneic melanomas, but not the HLA-A2- melanomas. They also did not lyse the HLA-A2+ non-melanoma cell lines. The RP-HPLC separations of reconstituting fractions revealed three peaks (fractions) of reconstitution.

CONCLUSION

These results showed that peptides derived from three active fractions were related to human melanoma-specific peptide antigens recognized by HLA-A2-restricted TIL.

Ligand induction of a transcriptionally active thyroid hormone receptor coactivator complex

Transcriptional regulation by nuclear hormone receptors is thought to involve interactions with putative cofactors that may potentiate receptor function. Here we show that human thyroid hormone receptor alpha purified from HeLa cells grown in the presence of thyroid hormone (T3) is associated with a group of distinct nuclear proteins termed thyroid hormone receptor-associated proteins (TRAPs). In an in vitro system reconstituted with general initiation factors and cofactors (and in the absence of added T3), the "liganded" thyroid hormone receptor (TR)/TRAP complex markedly activates transcription from a promoter template containing T3-response elements. Moreover, whereas the retinoid X receptor is not detected in the TR/TRAP complex, its presence is required for the function of the complex. In contrast, human thyroid hormone receptor alpha purified from cells grown in the absence of T3 lacks the TRAPs and effects only a low level of activation that is dependent on added ligand. These findings demonstrate the ligand-dependent in vivo formation of a transcriptionally active TR-multisubunit protein complex and suggest a role for TRAPs as positive coactivators for gene-specific transcriptional activation.

Isolation and characterization of two human transcription factor IIH (TFIIH)-related complexes: ERCC2/CAK and TFIIH

Transcription factor IIH (TFIIH) is a multisubunit protein complex essential for both the initiation of RNA polymerase class II (pol II)-catalyzed transcription and nucleotide excision repair of DNA. Recent studies have shown that TFIIH copurifies with the cyclin-dependent kinase (cdk)-activating kinase complex (CAK) that includes cdk7, cyclin H, and p36/MAT1. Here we report the isolation of two TFIIH-related complexes: TFIIH* and ERCC2/CAK. TFIIH* consists of a subset of the TFIIH complex proteins including ERCC3 (XPB), p62, p44, p41, and p34 but is devoid of detectable levels of ERCC2 (XPD) and CAK. ERCC2/CAK was isolated as a complex that exhibits CAK activity that cosediments with the three CAK components (cdk7, cyclin H, and p36/MAT1) as well as the ERCC2 (XPD) protein. TFIIH* can support pol II-catalyzed transcription in vitro with lower efficiency compared with TFIIH. This TFIIH*-dependent transcription reaction was stimulated by ERCC2/CAK. The ERCC2/CAK and TFIIH* complexes are each active in DNA repair as shown by their ability to complement extracts prepared from ERCC2 (XPD)- and ERCC3 (XPB)-deficient cells, respectively, in supporting the excision of DNA containing a cholesterol lesion. These data suggest that TFIIH* and ERCC2/CAK interact to form the TFIIH holoenzyme capable of efficiently assembling the pol II transcription initiation complex and directly participating in excision repair reactions.

Detection and evaluation of p53 intron 2 polymorphism in lung carcinomas in Hong Kong

A polymorphism in intron 2 of the p53 gene, which gives rise to 2 alleles, A1 and A2, was analyzed by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and direct DNA-sequencing techniques. The distribution of this allele in the peripheral blood in the Chinese population comprising 27 healthy individuals, 30 bronchiectasis patients, 34 non-small-cell lung cancer (NSCLC) patients and 27 SCLC patients was analyzed. The genotypic distributions for this marker were significantly different between the blood of healthy individuals and SCLC patients. There was no significant difference between genotypes of Caucasians and Chinese. Tumors, normal lungs and peripheral blood of 83 adenocarcinoma and 10 squamous cell carcinoma patients were also studied. There was a significant difference in the distribution of the genotypes detected in tumor tissues vs. blood of adenocarcinoma patients. The frequency of detection of the A1/A1 genotype in the tumor tissues was increased in adenocarcinoma patients as compared with the blood of adenocarcinoma patients and was decreased in the blood of SCLC patients as compared with the blood of healthy individuals. Survival rates in Hong Kong adenocarcinoma patients with the A1/A1 genotype were lower than those in patients with A1/A2 and A2/A2 genotypes up to 30 months post-operation. Point mutations were detected at the p53 intron 2 polymorphic locus in NSCLC specimens, with a mutation rate of 15.4% (8/52). All mutations were GC transversions. The significance of this instability in p53 intron 2 remains to be elucidated.

TATA-binding protein residues implicated in a functional interplay between negative cofactor NC2 (Dr1) and general factors TFIIA and TFIIB

The TATA-binding protein (TBP) plays a key role in transcription initiation. Several negative cofactors (NC1, NC2, and Dr1) are known to interact with TBP in a manner that prevents productive interactions of transcription factors TFIIA and TFIIB with promoter-bound TBP. To gain insights into the regulatory interplay on the surface of TBP, we have employed mutant forms of TBP to identify amino acid residues important for interactions with the negative regulatory cofactor NC2 and the general factor TFIIB. The results show the involvement of distinct domains of TBP in these interactions. Residues (Lys-133, Lys-145, and Lys-151) in the basic repeat region are important for interactions with NC2, as well as with TFIIA (Buratowski, S., and Zhou, H. (1992) Science 255, 1130-1132; Lee, D. K., DeJong, J., Hashimoto, S., Horikoshi, M., and Roeder, R. G. (1992) Mol. Cell. Biol. 12, 5189-5196), whereas a residue (Leu-189) in the second stirrup-like loop spanning S2' and S3' is required for interaction with TFIIB. In addition, we demonstrate that NC2 is identical to the previously cloned negative cofactor Dr1. The implications of these results for TBP structure and function are discussed.

Phosphorylation negatively regulates the function of coactivator PC4

Human positive cofactor 4 (PC4) mediates activator-dependent transcription by RNA polymerase II, apparently through interactions with transcriptional activators and the basal transcription machinery. We report here that PC4 function is modulated by in vivo phosphorylation. Protein-protein interaction studies and in vitro transcription assays demonstrate that only the nonphosphorylated form of PC4 is functionally active. Although recombinant PC4 can be phosphorylated by casein kinase II and protein kinase C in vitro, mutational and mass spectrometric analyses suggest that the in vivo hyperphosphorylation of PC4 is mediated mainly by casein kinase II and restricted to an N-terminal serine-rich region. These observations provide one example of a transcriptional cofactor that is negatively regulated by casein kinase II phosphorylation.

Purification, cloning, and characterization of a human coactivator, PC4, that mediates transcriptional activation of class II genes

Activator-dependent transcription in mammalian cells requires upstream stimulatory activity (USA)-derived cofactors in addition to those present in TFIID. A novel positive cofactor (PC4) purified from the human USA fraction effected a marked enhancement (up to 85-fold) of GAL4-AH-dependent transcription in conjunction with TFIID and other general factors. Isolation of a corresponding cDNA identified PC4 as a 127 residue single-stranded DNA-binding protein with serine-rich regions near the N-terminus. Recombinant PC4 was functionally equivalent to native PC4, and both proteins markedly enhanced activation by diverse activation domains fused to the DNA-binding domain of GAL4. Recombinant PC4 interacted independently both with free or DNA-bound VP16 activation domains and with free or DNA-bound TFIIA-TBP complexes (but not with TBP alone). These results indicate that PC4 is a general coactivator that functions cooperatively with TAFs and mediates functional interactions between upstream activators and the general transcriptional machinery.

TATA-binding protein-associated factor(s) in TFIID function through the initiator to direct basal transcription from a TATA-less class II promoter

The RNA polymerase II (Pol II) basal transcription factor TFIID is composed of the TATA box-binding protein (TBP) and several TBP-associated factors (TAFs). TBP is required for Pol II transcription from TATA-containing and TATA-less promoters. TATA-less promoters of mRNA-encoding genes often contain an initiator element at the transcription start site that is sufficient to direct accurate Pol II transcription. Here we address the mechanisms of functional TBP recruitment to the TATA-less initiator-dependent promoter of the mouse terminal deoxynucleotidyl transferase (TdT) gene. We show that the natural TATA-less TdT initiator region is sufficient to promote low levels of specific transcription in vitro and to direct the assembly of a stable preinitiation complex. In contrast to what is observed for several other promoters lacking a consensus TATA element, the TATA-binding activity of TBP is not required for the functional recruitment of TFIID to the natural TATA-less TdT and beta-polymerase promoters. Moreover, a comparison of TBP and highly purified epitope-tagged TFIID reveals that one or several TAFs function independently of distal regulatory elements to mediate initiator-directed (basal) transcription from the natural TATA-less TdT core promoter in crude nuclear extracts. Furthermore, by using a transcription system reconstituted with purified components, we present the first evidence for a basal transcription function of TAFs through the TdT initiator element. Altogether, our results suggest an alternative pathway for TFIID recruitment to initiator-dependent TATA-less class II promoters in which TAF(s) recruit TBP by interacting either directly or indirectly with the initiator region.

The high mobility group protein HMG1 can reversibly inhibit class II gene transcription by interaction with the TATA-binding protein

Regulation of transcription by RNA polymerase II in eukaryotic cells requires both basal and accessory factors, which interact through specific protein-DNA or protein-protein interactions. The high mobility group 1 protein (HMG1) was previously demonstrated to be a nonhistone chromatin-associated protein, which selectively recognizes cruciform DNA rather than a specific primary sequence element. During our investigations of proteins that interact with TFIID, we found that purified mammalian HMG1, as well as recombinant human HMG1, can interact with TATA-binding protein (TBP) in the presence of a TATA box-containing oligonucleotide to form a specific HMG1.TBP.promoter complex. This complex prevents TFIIB binding to TBP and consequently blocks formation of the preinitiation complex. In contrast, TFIIA can compete with HMG1 for binding to TBP. In an in vitro transcription assay reconstituted with highly purified or recombinant general factors, HMG1 is able to inhibit transcription by RNA polymerase II over 30-fold. As expected, addition of TFIIA can partially reverse this repression in a concentration-dependent manner. These results demonstrate that HMG1, a chromatin-associated protein, has the potential to act as a TBP-dependent negative transcription factor and may provide an important link between chromatin structure and the modulation of class II gene transcription.

Unique TATA-binding protein-containing complexes and cofactors involved in transcription by RNA polymerases II and III

Two multisubunit complexes containing the TATA-binding protein (TBP) were isolated from HeLa cells constitutively expressing the FLAG epitope-tagged TBP using antibody affinity and peptide elution methods. One of the complexes (f:TFIID), isolated from the P11 0.85 M KCl fraction, contains at least 13 specific TBP-associated factors (TAFs) and can mediate activator-dependent transcription by RNA polymerase II. Importantly, activator function through the highly purified f:TFIID complex still requires a general cofactor fraction containing upstream factor stimulatory activity (USA). As previously observed with partially purified activator-competent natural TFIID, f:TFIID generates extended TATA-dependent footprints on the intrinsically strong adenovirus major late promoter (MLP) but only restricted footprints on the weak adenovirus E1b and E4 and HIV (core) promoters. Along with previous demonstrations of activator-induced downstream TFIID interactions on the E4 promoter, these results argue for a relationship between downstream interactions and overall promoter strength. Initiator-like sequences appear not to be essential for downstream interactions since they have no effect on downstream MLP interactions when mutated, do not effect downstream interactions on the HIV promoter and are not present on the inducible E4 promoter. The other multisubunit complex (f:TFIIIB), isolated from the P11 0.30 M KCl fraction, contains four specific TAFs and can substitute for one of the fractions (TFIIIB) required for RNA polymerase III (pol III) transcription. Neither f:TFIID nor TBP could substitute for this pol III TBP-containing fraction. This plus the fact that f:TFIIIB failed to generate a footprint on the MLP underscores the importance of TAFs in determining promoter specificity by different RNA polymerases.