[PSI+] (Sup35p); [URE3] (Ure2p); [PIN+] or [RNQ+] (Rnq1p); [SWI1+] (Swi1p) and [OCT8+] (Cyc8p)
Prion HET-s from Podospora anserina
Neuron-specific isoform of CPEB from Aplysia californica (marine snail)

Structure
Amyloids are formed of long unbranched fibers that are characterized by an extended beta-sheet secondary structure in which individual beta strands (β-strands) (coloured arrows in the adjacent figure) are arranged in an orientation perpendicular to the long axis of the fiber. Such a structure is known as cross-β structure. Each individual fiber may be 7–13 nanometres in width and a few micrometres in length. The main hallmarks recognised by different disciplines to classify protein aggregates as amyloid is the presence of a fibrillar morphology with the expected diameter, detected using transmission electron microscopy (TEM) or atomic force microscopy (AFM), the presence of a cross-β secondary structure, determined with circular dichroism, FTIR, solid-state nuclear magnetic resonance (ssNMR), X-ray crystallography, or X-ray fiber diffraction (often considered the "gold-standard" test to see whether a structure contains cross-β fibres), and an ability to stain with specific dyes, such as Congo red, thioflavin T or thioflavin S.The term "cross-β" was based on the observation of two sets of diffraction lines, one longitudinal and one transverse, that form a characteristic "cross" pattern. There are two characteristic scattering diffraction signals produced at 4.7 and 10 Ångstroms (0.47 nm and 1.0 nm), corresponding to the interstrand and stacking distances in beta sheets. The "stacks" of beta sheet are short and traverse the breadth of the amyloid fibril; the length of the amyloid fibril is built by aligned β-strands.
Mechanism of action
The causes of migraine are not clearly understood; however, the efficacy of naratriptans and other triptans is believed to be due to their activity as 5-HT (serotonin) agonists. Society and culture
In the United States, the Food and Drug Administration (FDA) approved naratriptan on February 11, 1998. It was covered by U.S. Patent no. 4997841; the FDA lists the patent as expiring on July 7, 2010.In July 2010, in the wake of the patent expiration, several drug manufacturers, including Roxane Labs, Sandoz and Teva Pharmaceuticals, announced that they were launching generic Naratriptan medications. The drug continued to be covered by European patent 0303507 in Germany, Spain, France and the United Kingdom through March 10, 2012, and by Australian patent 611469 in Australia through June 17, 2013. It had previously been covered by Canadian patent 1210968; but both Sandoz and Teva (formerly Novopharm) have offered generic equivalents in Canada since that patents expiration December 1, 2009.On December 23, 2014, in response to a request from Health Canada, importers in Canada agreed to quarantine the importation of health products, including generic Naratriptan manufactured for both Sandoz and Teva, from Dr. Reddys Laboratories in Srikakulam, India. Because Teva and Sandoz are the only approved suppliers of generic Naratriptan in Canada, the quarantine resulted in Naratriptan being placed on the Canadian drug shortage list.Following the Canadian quarantine, the United Arab Emirates Ministry of Health also imposed a similar quarantine. == References ==