Topological characteristics of chromatin in a cell-free system from Drosophila embryos

BACKGROUND: Vasoactive intestinal polypeptide (VIP)-secreting tumors of the pancreas represent a rare subtype of pancreatic islet cell tumors with an estimated incidence of 0.2 to 0.5 per million per year. We provide data on a relatively large series of patients with VIP-secreting tumors and review current literature regarding this specific entity. METHODS: A retrospective review was performed of all patients with VIP-secreting tumors of the pancreas treated from 1977 to 1992 at our institution. Presenting signs, symptoms, mode of diagnosis, extent of disease, surgical resectability, tumor size, treatments, hormone levels, and survival were assessed. RESULTS: Eighteen patients were identified, 9 male and 9 female. Ages ranged from 23 to 74 years (mean 51 years). Secretory diarrhea was the most common symptom, occurring in 16 of 18 patients (89%). The most common tumor location was the tail of the pancreas (9 patients). Fourteen patients (78%) had liver metastasis at diagnosis. Curative resections were attempted in only 5 patients (28%). The mean survival was 3.6 years with the longest disease-free survival being 15 years and longest overall survival 15 years. CONCLUSIONS: VIP-secreting tumors are extremely rare entities and usually metastatic at the time of diagnosis. Despite advanced disease, these patients can have extended survival.     

Topological characterization of the essential Escherichia coli cell division protein FtsN

Genetic and biochemical approaches were used to analyze a topological model for FtsN, a 36-kDa protein with a putative transmembrane segment near the N terminus, and to ascertain the requirements of the putative cytoplasmic and membrane-spanning domains for the function of this protein. Analysis of FtsN-PhoA fusions revealed that the putative transmembrane segment of FtsN could act as a translocation signal. Protease accessibility studies of FtsN in spheroblasts and inverted membrane vesicles confirmed that FtsN had a simple bitopic topology with a short cytoplasmic amino terminus, a single membrane-spanning domain, and a large periplasmic carboxy terminus. To ascertain the functional requirements of the N-terminal segments of FtsN, various constructs were made. Deletion of the N-terminal cytoplasmic and membrane-spanning domains led to intracellular localization of the carboxy domain, instability,and loss of function. Replacement of the N-terminal cytoplasmic and membrane-spanning domains with a membrane-spanning domain from MalG restored subcellular localization and function. These N-terminal domains of FtsN could also be replaced by the cleavable MalE signal sequence with restoration of subcellular localization and function. It is concluded that the N-terminal, cytoplasmic, and transmembrane domains of FtsN are not required for function of the carboxy domain other than to transport it to the periplasm. FtsQ and FtsI were also analyzed.