Shade-establishing plants growing in the forest understory are exposed to constant high light or fluctuating light when gaps are created by fallen trees. Our previous studies indicate that photosystem I (PSI) is sensitive to constant high light in shade-establishing tree species, however, the effects of fluctuating light on PSI and photosystem II (PSII) in shade-establishing species are little ...

The yeast [PSI+] prion is an epigenetic modifier of translation termination fidelity that causes nonsense suppression. The prion [PSI+] forms when the translation termination factor Sup35p adopts a self-propagating conformation. The presence of the [PSI+] prion modulates survivability in a variety of growth conditions. Nonsense suppression is essential for many [PSI+]-mediated phenotypes, but m...

Photosystem I (PSI) is a photochemically active membrane protein complex that functions at the reducing site of the photosynthetic electron-transfer chain as plastocyanin-ferredoxin oxidoreductase. PsaE, a peripheral subunit of the PSI complex, plays an important role in the function of PSI. PsaE is involved in the docking of ferredoxin/flavodoxin to the PSI complex and also participates in the...

We have used a strategy for colocalization of Psi (Psi)-tethered ribozymes and targets to demonstrate that Psi sequences are capable of specific interaction in the cytoplasm of both packaging and nonpackaging cells. These results indicate that current in vitro dimerization models may have in vivo counterparts. The methodology used may be applied to further genetic analyses on Psi domain interac...

Photosystem I-light harvesting complex I (PSI-LHCI) was isolated from the thermoacidophilic red alga Galdieria sulphuraria, and its structure, composition, and light-harvesting function were characterized by electron microscopy, mass spectrometry, and ultrafast optical spectroscopy. The results show that Galdieria PSI is a monomer with core features similar to those of PSI from green algae, but...

Light regulation of photosystem I (PSI) biogenesis was studied in a unicellular green alga, Chlamydomonas reinhardtii. When Chlamydomonas cells were transferred from darkness to the light, mRNAs for both nuclear- and chloroplast-encoded PSI subunits were induced in concert. This light induction was inhibited by photosynthetic electron transport (PET) inhibitors, 3-(3,4 dichlorophenyl)-1,1-dimet...

The formation of pseudouridine (psi) in human U1, U2 and U5 small nuclear RNAs (snRNAs) was investigated using HeLa cell extracts. Unmodified snRNAs were synthesized in vitro and the extent of psi formation was determined after incubation in cell extracts. The formation of psi on labelled substrates was monitored in the presence of 5-fluorouracil (5-FU)-containing snRNAs as inhibitors of psi fo...

Replication of amyloid-based yeast prions [PSI(+)], [URE3], and [PIN(+)] depends on the protein disaggregation machinery that includes Hsp104, Hsp70, and Hsp40 molecular chaperones. Yet, overexpressing Hsp104 cures cells of [PSI(+)] prions. An Hsp70 mutant (Ssa1-21p) antagonizes propagation of [PSI(+)] in a manner resembling elevated Hsp104. The major cytosolic Hsp40 Sis1p is the only Hsp40 req...

The maintenance of [PSI], a prion-like form of the yeast release factor Sup35, requires a specific concentration of the chaperone protein Hsp104: either deletion or overexpression of Hsp104 will cure cells of [PSI]. A major puzzle of these studies was that overexpression of Hsp104 alone, from a heterologous promoter, cures cells of [PSI] very efficiently, yet the natural induction of Hsp104 wit...

The [PSI(+)] nonsense-suppressor determinant of Saccharomyces cerevisiae results from the ability of Sup35 (eRF3) translation termination factor to undergo prion-like aggregation [1]. Although this process is autocatalytic, in vivo it depends on the chaperone Hsp104, whose lack or overexpression can cure [PSI(+)] [2]. Overproduction of the chaperone protein Ssb1 increased the [PSI(+)] curing by...