The cardiac troponin T pre-mRNA contains an exonic splicing enhancer that is required for inclusion of the alternative exon 5. Here we show that enhancer activity is exquisitely sensitive to changes in the sequence of a 9-nucleotide motif (GAGGAAGAA) even when its purine content is preserved. A series of mutations that increased or decreased the level of exon inclusion in vivo were used to correlate enhancer strength with RNA-protein interactions in vitro. Analyses involving UV cross-linking and immunoprecipitation indicated that only four (SRp30a, SRp40, SRp55, and SRp75) of six essential splicing factors known as SR proteins bind to the active enhancer RNA. Moreover, purified SRp40 and SRp55 activate splicing of exon 5 when added to a splicing-deficient S100 extract. Purified SRp30b did not stimulate splicing in S100 extracts, which is consistent with its failure to bind the enhancer RNA. In vitro competition of SR protein splicing activity and UV cross-linking demonstrated that the sequence determinants for SR protein binding were precisely coincident with the sequence determinants of enhancer strength. Thus, a subset of SR proteins interacts directly with the exonic enhancer to promote inclusion of a poorly defined alternative exon. Independent regulation of the levels of SR proteins may, therefore, contribute to the developmental regulation of exon inclusion.Pre-mRNA splicing involves two transesterification reactions mediated by the spliceosome (11, 21). The mechanisms by which exon-intron borders are first defined within complex pre-mRNAs remain largely unknown. Although splice donor and acceptor sequences are fairly well conserved among premRNAs, these elements are not sufficient to distinguish bona fide splice sites from unused cryptic splice sites present in many metazoan pre-mRNAs. Because splicing is so precise, additional controls for splice site selection must be present elsewhere in the pre-mRNA.Results with vertebrate and invertebrate experimental systems have demonstrated that sequences within exons, exclusive of splice junctions, can play a role in splice site selection (13). One positively acting splicing element is a 13-nucleotide repeat in the female-specific exon of the Drosophila doublesex (dsx) gene. Two proteins, transformer-2 and transformer, promote utilization of an upstream 3Ј splice site via direct interactions with the repeats (12,15,22). Purine-rich splicing elements, called splicing enhancers, have recently been identified in several vertebrate exons (1,6,16,19,28,31,33,35,36) and in the dsx female-specific exon (20). Splicing enhancers are required for efficient splicing of the resident exon, and several have been shown to enhance splicing of heterologous exons (16,19,33,35,36). With one exception (16), splicing enhancers appear to activate splicing of the upstream intron (35). The enhancer in the fibronectin ED1 exon has been shown to promote binding of the U2 small nuclear ribonucleoprotein particle (snRNP) to the upstream branch site (19), which is consistent with this observ...

HID subtyping did not provide useful information to the clinician or the pathologist. The data are consistent with the notion that the pattern, extent, and severity of atrophy with/without intestinal metaplasia is a far more important predictor of increased cancer risk than intestinal metaplasia subtype.

Helicobacter pylori infection was examined among 356 asymptomatic white Hispanic and black children aged 2--16 years attending 13 licensed day care centers in Houston. Demographic information and socioeconomic factors were evaluated. H. pylori status was determined by (13)C-urea breath testing. The prevalence of active H. pylori infection was 24% and increased with age. Prevalence was almost identical among white Hispanic and black children. Children living in the most crowded conditions were at the greatest risk for H. pylori acquisition, and an inverse correlation was seen between the mother's education and H. pylori positivity in children. Breast-feeding played a protective role against the acquisition of H. pylori infection. Understanding the epidemiology of H. pylori infection in childhood requires better understanding of the interactions between environment, ethnic group, and socioeconomic conditions.

Among asymptomatic children, there is a wide variation in the prevalence of H. pylori infection based on the diagnostic test used. The study shows that antibody assays are less suitable than the UBT. However, under certain conditions, the IgG assays (combined systemic, salivary, or both) are less expensive alternative tools to the UBT for epidemiological studies in children.

Background-There have been conflicting reports concerning the use of cardia biopsies in screening patients for gastrooesophageal disease. Aim-To define the histopathological changes in the gastric cardia of patients with and without gastro-oesophageal disease. Methods-Topographically mapped gastric biopsy specimens were obtained from patients with gastro-oesophageal disease and from controls. Biopsies were scored on a visual analogue scale of 0 to 5 for Helicobacter pylori, intestinal metaplasia, pancreatic metaplasia, foveolar hyperplasia, and active inflammation. The presence or absence of cardiac glands was recorded. Results-Sixty five patients with gastrooesophageal disease and 71 controls were examined. Intestinal metaplasia was present in cardia biopsies of 10 patients with gastro-oesophageal disease and 11 controls. Only two patients with gastrooesophageal disease and intestinal metaplasia in the cardia had no evidence of exposure to H pylori. Intestinal metaplasia was not found in the cardia of those with long segment Barrett's oesophagus. Carditis was strongly associated with active H pylori infection (p = 0.000) and resolved after treatment of the infection. A negative association was present between gastro-oesophageal disease and the presence of cardiac glands in cardiac biopsies (p = 0.003). Pancreatic metaplasia was found in 15 of 65 and foveolar hyperplasia in 19 of 65 cases but neither was related to gastro-oesophageal disease. Conclusion-Intestinal metaplasia in the cardia is uncommon in gastrooesophageal disease in the absence of H pylori infection. With chronic H pylori infection the junction between the cardia and corpus expands in a cardia-corpal direction. (J Clin Pathol 2000;53:619-625)