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Biomedical subjects

S Dalton

Publications and source records attributed to S Dalton.

At least 37 records · Page 2Linked to original sources
PubMed1994

Mapping of the human SAP1 (SRF accessory protein 1) gene and SAP2, a gene encoding a related protein, to chromosomal bands 1q32 and 12q23, respectively.

SAP1, SAP2, and ELK1 form a related subgroup of ETS-domain proteins that can form ternary complexes with the transcription factor SRF at the c-fos serum response element (SRE). SAP1 was identified by a genetic screen for proteins interacting with SRF expressed in yeast, and SAP2 by its homology with SAP1; ELK1 was previously identified by its homology to the ETS domain. cDNA probes were used to isolate cosmid and phage clones harboring genes encoding SAP1 and SAP2. These clones were subsequently used to map the genes to 1q32 and 12q23, respectively, by fluorescence in situ hybridization.

Chromosome Mapping↗
PubMed1993

Isolation and characterization of SRF accessory proteins.

Many genes which are regulated by growth factors contain a common regulatory element, the serum response element (SRE). Activation of transcription by the SRE involves a ternary complex formed between a ubiquitous factor, serum response factor (SRF), and a second protein, p62/TCF. We used a yeast genetic screen to isolate cDNAs encoding a protein, SAP-1, with the DNA binding properties of p62/TCF. The SAP-1 sequence contains three regions of homology to the previously uncharacterized Elk-1 protein, which also acts as an SRF accessory protein. Only two of these regions are required for cooperative interactions with SRF in the ternary complex. The third contains several conserved sites for the MAP kinases, whose activity is regulated in response to growth factor stimulation. We discuss the potential role of these proteins in regulation of the c-fos SRE.

Amino Acid Sequence↗
PubMed1993

Functional analysis of a growth factor-responsive transcription factor complex.

Serum response factor (SRF) forms a ternary complex at the c-fos serum response element (SRE) with an accessory factor, Elk-1. We constructed altered-binding specificity derivatives of SRF and Elk-1 that form a ternary complex at a mutated, inactive SRE; like Elk-1, the Elk-1 variant only binds its target as part of a ternary complex with SRF. Simultaneous expression of these SRF and Elk-1 derivatives restores serum-regulated activity to the mutated SRE in transfected cells. Efficient transcriptional activation is dependent on the regulated phosphorylation of Elk-1 C-terminal MAP kinase sites and requires the C-terminal sequences of SRF as well as SRF sequences that mediate ternary complex formation. These experiments provide direct evidence that SRF and Elk-1 functionally cooperate in the ternary complex at the SRE to regulate transcription.

3T3 Cells↗
PubMed1993

Factors predicting death, survival and functional outcome in a prospective study of early rheumatoid disease over fifteen years.

Sixty-four survivors from a prospective study of early rheumatoid disease were assessed again at a mean of 15.2 years from presentation and their status compared with 29 patients who had died. Eleven of the dead and only two of the survivors had been treated with steroids. There was a small increase in mortality due to the disease itself but only one death was directly caused by it. As might be expected, those who died were older. In the first year of disease, they had lower haemoglobin levels, a lower body mass, higher sedimentation rates and higher levels of blood urea. One-fifth at entry to the study and two-fifths by the time of death, had poor functional capacity. Of 64 survivors, six had poor functional capacity at entry and nine after 15 years. Discriminant analysis was performed to identify the most powerful combination of early features predicting a poor functional outcome. A combination including early erosive change, seropositivity, poor grip strength and cervical subluxation predicted the outcome correctly in 73% of survivors. Almost 60% of survivors remained with or improved to normal function at 15 years suggesting that morbidity is not as bad as has been suggested in the past.

Adult↗
PubMed1993

Obesity surgery: dietary and psychosocial expectations and reality.

Psychosocial and dietary habits have been compared in patients considering (Pre n = 33) or who had (Post n = 32) surgery for morbid obesity. Failure of conventional diets was attributed to lack of self-discipline (Pre 92% [22/24] vs. Post 87% [20/23], NS). Consumption of fast foods fell (Pre 70% [23/33] vs. Post 16% [5/32], p < 0.0001). Preoperative patients had unrealistic social expectations. They exaggerated the prospect of improved friendship (Pre 67% [22/32] vs. Post 34% [11/21], p < 0.05), erroneously anticipated better sex (Pre 78% [25/32] vs. Post 50% [15/30], p < or = 0.05), predicted better acceptance at work (Pre 85% [23/27] vs. Post 50% [15/30], p < or = 0.05), and misanticipated improved relationship with their partner (Pre 77% [20/26] vs. Post [47% 8/17], p < or = 0.05). Two factors predicted becoming employed following surgery: age (became employed [n = 5] 28 +/- 2 years vs. remained unemployed [n = 12] 44 +/- 4 years, p < 0.05) and percentage of excess weight lost (became employed 76 +/- 11 vs. remained unemployed 51 +/- 7, p < 0.05). The free support group was "useful" (17/17), yet only 5% attended regularly. Patients considering obesity surgery had specific unrealistic psychosocial expectations. They infrequently availed themselves of postoperative professional help. We identify the features associated with gaining employment.

Adult↗
PubMed1992

Transcriptional activation by the human c-Myc oncoprotein in yeast requires interaction with Max.

The c-myc protein (Myc) contains an amino-terminal transcriptional activation domain and a carboxy-terminal basic helix-loop-helix-leucine zipper (bHLH-Z) domain that directs dimerization of Myc with its partner, the max protein (Max), and promotes DNA binding to sites containing a CACGTG core consensus sequence. Despite these characteristics and the observation that Myc can modulate gene expression, a direct role for Myc or Max as transcription factors has never been demonstrated. Here we use Saccharomyces cerevisiae as an in vivo model system to show that the Myc protein is a sequence-specific transcriptional activator whose DNA binding is strictly dependent on dimerization with Max. Transactivation is mediated by the amino-terminal domain of Myc. We find that Max homodimers bind to the same DNA sequence as Myc+Max but that they fail to transactivate and thus can antagonize Myc+Max function. We also show that the Max HLH-Z domain has a higher affinity for the Myc HLH-Z domain than for itself, and suggest that the heterodimeric Myc+Max activator forms preferentially at equilibrium.

Base Sequence↗
PubMed1992

Characterization of SAP-1, a protein recruited by serum response factor to the c-fos serum response element.

We used a yeast genetic screen to isolate cDNAs that encode a protein, SRF accessory protein-1 (SAP-1), that is recruited to the c-fos serum response element (SRE) as part of a ternary complex that includes serum response factor (SRF). SAP-1 requires DNA-bound SRF for ternary complex formation and makes extensive DNA contacts to the 5' side of SRF, but does not bind DNA autonomously. Ternary complex formation by SAP-1 requires only the DNA-binding domain of SRF, which can be replaced by that of the related yeast protein MCM1. We isolated cDNAs encoding two forms of SAP-1 protein, SAP-1a and SAP-1b, which differ at their C termini. Both SAP-1 proteins contain three regions of striking homology with the elk-1 protein, including an N-terminal ets domain. Ternary complex formation by SAP-1 requires both the ets domain and a second conserved region 50 amino acids to its C-terminal side. SAP-1 has similar DNA binding properties to the previously characterized HeLa cell protein p62/TCF.

Amino Acid Sequence↗
PubMed1992

Cell cycle regulation of the human cdc2 gene.

Transcription of the human cdc2 gene is cell cycle regulated and restricted to proliferating cells. Nuclear run-on assays show that cdc2 transcription is high in S and G2 phases of the cell cycle but low in G1. To investigate transcriptional control further, genomic clones of the human cdc2 gene containing 5' flanking sequences were isolated and shown to function as a growth regulated promoter in vivo when fused to a CAT reporter gene. In primary human fibroblasts, the human cdc2 promoter is negatively regulated by arrest of cell growth in a similar fashion to the endogenous gene. This requires specific 5' flanking upstream negative control (UNC) sequences which mediate repression. The retinoblastoma susceptibility gene product (Rb) specifically represses cdc2 transcription in cycling cells via 136 bp of 5' flanking sequence located between -245 and -109 within the UNC region. E2F binding sites in this region were shown to be essential for optimal repression. A model is proposed where Rb negatively regulates the cdc2 promoter in non-cycling and cycling G1 cells.

Base Sequence↗
PubMed1989

Transcription from the intron-containing chicken histone H2A.F gene is not S-phase regulated.

The nucleotide sequence of an 8.2 kb BamHI fragment containing the entire chicken histone H2AF gene has been determined. Unlike the majority of histone genes, the coding region is interrupted by four intervening sequences. While sequencing the 8.2 kb BamHI fragment it was found that the promoter and first exon of an unidentified non-histone gene lies immediately downstream of the H2AF gene. Studies of H2AF gene transcription show that, unlike the major core and H1 histone genes, it is not coupled to DNA synthesis.

Amino Acid Sequence↗
PubMed1989

Transforming growth factor alpha: an aromatic side chain at position 38 is essential for biological activity.

Site-directed mutagenesis has been performed in the human transforming growth factor alpha gene. When tyrosine 38 is mutated into phenylalanine or tryptophane, biological activity is retained. In contrast, other alterations between cysteine 34 and cysteine 43 and disruption of disulfide bonds 8 to 21 and 34 to 43 resulted in loss of activities. The presence of an aromatic side chain at position 38 of transforming growth factor alpha seems to be essential for its activity.

Amino Acid Sequence↗
PubMed1988

Conservation of histone H2A/H2B intergene regions: a role for the H2B specific element in divergent transcription.

The organization and function of potential regulatory elements associated with the promoters of chicken H2A and H2B genes pairs have been examined. The intergene regions of six dispersed and divergently-transcribed H2A/H2B gene pairs contain several extremely well conserved and spaced blocks of sequence homology. Adjacent coding regions are on average 342 base-pairs apart. Respective TATA boxes are separated by 180 base-pairs and within this confined region there are four CCAAT boxes and a previously identified 13 base-pair H2B-specific element (H2B-box) which has homology to the octamer motif present in a number of gene promoter/enhancer elements. Transcription of H2A and H2B genes from wild-type and mutant constructs was measured in transient assays by transfection into HeLa cells, and in permanently transformed clonal cell lines. In vitro separation of the two genes at a unique intergenic site significantly decreased transcription of each gene. This suggested that the H2A/H2B gene pairs contained overlapping promoters. Deletion or point mutagenesis of the H2B-specific element decreased the levels of H2B and the H2A transcripts indicating that this sequence is a common regulatory element of both genes in the divergent-pair configeration.

Animals↗
PubMed1988

A gene-specific promoter element is required for optimal expression of the histone H1 gene in S-phase.

An H1 gene-specific element (H1-box, 5'-AAACACA-3') modulates S-phase expression of the gene in vivo as judged by analysis of transcripts from histone genes transfected into HeLa cells. Deletion or base-substitution of the element causes a 15- to 30-fold decrease in steady-state H1 mRNA levels in randomly growing cells and eliminates cell cycle control of transcription in synchronized cells. Mutations within the H1-specific element which abolish S-phase control of transcription also eliminate binding of a sequence-specific nuclear factor capable of binding specifically to this region in vitro. Transfection of multiple copies of H1-box elements into cells drastically decreases H1 mRNA levels, mimicking the effect observed when the motif is rendered non-functional by deletion or substitution mutagenesis. In contrast, introduction of mutated H1 elements into cells has no detectable effect. Together, these results imply that an interaction between the H1-box and a sequence-specific trans-acting factor modulates transcriptional control of H1 genes in vivo.

Alpharetrovirus↗
PubMed1988

Maximal binding levels of an H1 histone gene-specific factor in S-phase correlate with maximal H1 gene transcription.

Levels of trans-acting factor (H1-SF) binding to the histone H1 gene-specific motif (5'-AAACACA-3' [L. S. Coles and J. R. E. Wells, Nucleic Acids Res. 13:585-594, 1985]) increase 12-fold from G1 to S-phase in synchronized cells and decrease again in G2 phase of the cell cycle. Since the H1 element is required for S-phase expression of H1 genes (S. Dalton and J. R. E. Wells, EMBO J. 7:49-56, 1988), it is likely that the increased levels of H1-SF binding component play an important role in S-phase regulation of H1 gene transcription.

Animals↗
PubMed1988

Transforming growth factor alpha: mutation of aspartic acid 47 and leucine 48 results in different biological activities.

To study the relationship between the primary structure of transforming growth factor alpha (TGF-alpha) and some of its functional properties (competition with epidermal growth factor (EGF) for binding to the EGF receptor and induction of anchorage-independent growth), we introduced single amino acid mutations into the sequence for the fully processed, 50-amino-acid human TGF-alpha. The wild-type and mutant proteins were expressed in a vector by using a yeast alpha mating pheromone promoter. Mutations of two amino acids that are conserved in the family of the EGF-like peptides and are located in the carboxy-terminal part of TGF-alpha resulted in different biological effects. When aspartic acid 47 was mutated to alanine or asparagine, biological activity was retained; in contrast, substitutions of this residue with serine or glutamic acid generated mutants with reduced binding and colony-forming capacities. When leucine 48 was mutated to alanine, a complete loss of binding and colony-forming abilities resulted; mutation of leucine 48 to isoleucine or methionine resulted in very low activities. Our data suggest that these two adjacent conserved amino acids in positions 47 and 48 play different roles in defining the structure and/or biological activity of TGF-alpha and that the carboxy terminus of TGF-alpha is involved in interactions with cellular TGF-alpha receptors. The side chain of leucine 48 appears to be crucial either indirectly in determining the biologically active conformation of TGF-alpha or directly in the molecular recognition of TGF-alpha by its receptor.

Amino Acid Sequence↗