FC0028
Ure2  -  Ure2 prion amyloid

Biological function
The [URE3] prion of Saccharomyces cerevisiae is an infectious amyloid form of Ure2.

Biochemical evidence
Five Ure2p variants in which the order of the amino acids in the prion domain was randomly shuffled while keeping the amino acid composition and C-terminal domain unchanged. Surprisingly, all five formed prions in vivo, with a range of frequencies and stabilities, and the prion domains of all five readily formed amyloid fibers in vitro. Ure2 forms prions primarily as a result of its sequence composition, as versions of Ure2 with the prion domain amino acids shuffled are still able to form prions. It was shown that prion induction by both Ure2 and Ure2-21, one of the scrambled versions of Ure2, is clearly dependent on the length of the inducing fragment. For Ure2-21p, no single sequence is found in all of the inducing fragments, highlighting the sequence independence of prion formation.

Structure/Mechanism
The Q/N content is 48%. Amino acids 59 – 65, which are expendable in the context of the full-length prion domain (PD), are necessary for induction in the context of the N-terminally truncated fragment Ure2. This observation clearly suggests some sort of length requirement.

Mechanism category
tethering

Significance
Sequence independence, but amino acid composition dependence of prion formation for Ure2 enables formation of alternative hydrogen bonding patterns. This may result in fibers with different stabilities and topologies.