Progressive amyloid deposition in senile plaques and cortical blood vessels may play a central role in the pathogenesis of Alzheimer disease. We have used x-ray diffraction and electron microscopy to study the molecular organization and morphology of macromolecular assemblies formed by three synthetic peptides homologous to fi protein of brain amyloid: fl-(1-28), residues 1-28 of the fi protein;[Ala"Jfl-(1-28), P-(1-28) with alanine substituted for lysine at position 16; and fl-(18-28), residues 18-28 of the fi protein.fl-(1-28) readily formed fibrils in vitro that were similar in ultrastructure to the in vivo amyloid and aggregated into large bundles resembling those ofsenile plaque cores. X-ray patterns from partially dried, oriented pellets showed a cross-fl-conformation. A series of small-angle, equatorial maxima were consistent with a tubular fibril having a mean diameter of 86 A and a wall composed of pairs of cross-fl-pleated sheets. The data may also be consistent with pairs ofcross-13-sheets that are centered 71-apart. [Ala]fl-(1-28) formed pleated sheet assemblies that were dissimilar to in vivo fibrils. The width of the to-A spacing indicated stacks of about six sheets. Thus, substitution of the uncharged alanine for the positively charged lysine in the fl-strand region enhances the packing of the sheets and dramatically alters the type of macromolecular aggregate formed. f8-(18-28) formed assemblies that had even a greater number of stacked sheets, w24 per diffracting domain as indicated by the sharp intersheet reflection. Our findings on these homologous synthetic assemblies help to define the specific sequence that is required to form Alzheimer-type amyloid fibrils, thus providing an in vitro model of age-related cerebral amyloidogenesis.The major histopathological features ofAlzheimer disease (AD) are neurofibrillary tangles, neuritic or senile plaques, and amyloid angiopathy (1). The plaques contain cores of extracellular proteinaceous filaments that have been identified as amyloid, based on their green birefringence after staining with Congo red and their 40-to 90-A diameter (2, 3). Structurally similar amyloid filaments also occur in the walls of some capillaries, arterioles, and small arteries in the cerebral cortex and in some meningeal arteries in patients with AD (4-10). These amyloid deposits are also found in the brains of Down syndrome patients over 30 years of age (11), as well as in the brains of aged normal humans (12) and lower mammals (13).The major proteinaceous component of amyloid both from the cerebral blood vessel walls and the plaque cores is an --4-kDa protein (8, 9, 14-17) designated the 3 protein (15) or A4 (8). The first 28 amino acids of this protein have been sequenced (7). A gene coding for the f3-amyloid protein has been mapped to chromosome 21 of the human genome (18)(19)(20), and the complete sequence of the putative precursor protein has been determined (21).The current study was carried out to investigate the amyloidogenic properties of peptides sharing se...

A rat thyroglobulin promoter fragment, capable of directing thyroid‐specific transcription, binds at least three different factors, TTF‐1, TTF‐2 and UFA, which are all present in nuclear extracts of the differentiated rat thyroid cell line FRTL‐5. TTF‐1 and TTF‐2 are FRTL‐5 specific, as demonstrated by their absence in nuclear extracts prepared from cell lines that do not express any thyroid‐differentiated function, while UFA is present in all cell lines tested. TTF‐1 has been extensively purified. It binds to the rat thyroglobulin promoter at three different sites which share sequence homology. Mutations in two of the three sites decrease both binding of TTF‐1 in vitro and promoter function in vivo. This suggests that the tissue‐specific expression of the thyroglobulin genes is mediated, at least in part, by the presence of a transcription factor exclusively in thyroid cells.

Epstein‐Barr virus (EBV) is unusual among DNA tumour viruses in that the virus particle is able to infect and immortalize resting cells with very high efficiency. Mutation of the viral genome has indicated that at least six viral genes (LMP‐1 and EBNAs 1, 2, 3A, 3C and LP) are essential for immortalization. We demonstrate that the activation of a G1 cyclin, cyclin D2, is an early event following infection with EBV and that cyclin D2 activation is dependent on the expression of viral genes. The different levels of cyclin D2 transcripts in Burkitt's lymphoma cell lines expressing different subsets of EBV immortalizing genes suggest an involvement of EBNA‐2 or EBNA‐LP in cyclin D2 regulation. By exposing resting primary B cells to a purified preparation of the EBV surface glycoprotein gp340, we have been able to achieve efficient expression of plasmid DNAs introduced by electroporation. Vectors encoding two viral genes, EBNA‐2 and EBNA‐LP, are sufficient to activate the expression of cyclin D2 in this system. Thus, the progression of resting B lymphocytes into the G1 phase of the cell cycle can be reconstituted in the absence of virus by the cooperation of two of the six viral genes required for immortalization.