Most life forms on Earth are supported by solar energy harnessed by oxygenic photosynthesis. In eukaryotes, photosynthesis is achieved by large membrane-embedded supercomplexes, containing reaction centers and connected antennae. Here, we report the structure of the higher plant PSI-LHCI super-complex determined at 2.8Å resolution. The structure includes 16 subunits and more than 200 prosthetic groups, which are mostly light harvesting pigments. The complete structures of the four LhcA subunits of LHCI include 52 chlorophyll a and 9 chlorophyll b molecules, as well as 10 carotenoids and 4 lipids. The structure of PSI-LHCI includes detailed protein pigments and pigment-pigment interactions, essential for the mechanism of excitation energy transfer and its modulation in one of nature's most efficient photochemical machines.

Most life forms on Earth are supported by solar energy harnessed by oxygenic photosynthesis. In eukaryotes, photosynthesis is achieved by large membrane-embedded super-complexes, containing reaction centers and connected antennae. Here, we report the structure of the higher plant PSI-LHCI super-complex determined at 2.8 Å resolution. The structure includes 16 subunits and more than 200 prosthetic groups, which are mostly light harvesting pigments. The complete structures of the four LhcA subunits of LHCI include 52 chlorophyll a and 9 chlorophyll b molecules, as well as 10 carotenoids and 4 lipids. The structure of PSI-LHCI includes detailed protein pigments and pigment–pigment interactions, essential for the mechanism of excitation energy transfer and its modulation in one of nature's most efficient photochemical machines.DOI: http://dx.doi.org/10.7554/eLife.07433.001

Replication-factor C (RFC) is a protein complex that loads the processivity clamp PCNA onto DNA. Elg1 is a conserved protein with homology to the largest subunit of RFC, but its function remained enigmatic. Here, we show that yeast Elg1 interacts physically and genetically with PCNA, in a manner that depends on PCNA modification, and exhibits preferential affinity for SUMOylated PCNA. This interaction is mediated by three small ubiquitin-like modifier (SUMO)-interacting motifs and a PCNA-interacting protein box close to the N-terminus of Elg1. These motifs are important for the ability of Elg1 to maintain genomic stability. SUMOylated PCNA is known to recruit the helicase Srs2, and in the absence of Elg1, Srs2 and SUMOylated PCNA accumulate on chromatin. Strains carrying mutations in both ELG1 and SRS2 exhibit a synthetic fitness defect that depends on PCNA modification. Our results underscore the importance of Elg1, Srs2 and SUMOylated PCNA in the maintenance of genomic stability.

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Telomeres, the natural ends of eukaryotic chromosomes, prevent the loss of chromosomal sequences and preclude their recognition as broken DNA. Telomere length is kept under strict boundaries by the action of various proteins, some with negative and others with positive effects on telomere length. Recently, data have been accumulating to support a role for DNA replication in the control of telomere length, although through a currently poorly understood mechanism. Elg1p, a replication factor C (RFC)-like protein of yeast, contributes to genome stability through a putative replication-associated function. Here, we show that Elg1p participates in negative control of telomere length and in telomeric silencing through a replication-mediated pathway. We show that the telomeric function of Elg1 is independent of recombination and completely dependent on an active telomerase. Additionally, this function depends on yKu and DNA polymerase. We discuss alternative models to explain how Elg1p affects telomere length.DNA replication ͉ replication factor C ͉ Saccharomyces cerevisiae R eplication of a linear DNA molecule is carried out by DNA polymerases and additional proteins that duplicate the DNA by moving coordinately on both the lagging and leading strands (1). DNA attrition at the ends of chromosomes due to the ''end replication problem'' is avoided by the action of the specialized reverse transcriptase, called telomerase (2, 3). Telomerase adds G-rich DNA repeats termed telomeres onto the ends of chromosomes. In addition to their role in preventing loss of chromosomal sequences, telomeres serve as a boarding pad for a multiprotein complex that is implicated in several important cellular functions. Among these functions is capping telomeres, thus avoiding the recognition of the natural ends of chromosomes as broken DNA. This capping in turn prevents cell cycle arrest and chromosomal fusions, allowing proper chromosomal segregation (4).Many proteins, most of which are part of the telomeric complex, regulate telomere length in both positive and negative fashions (5). The best-studied pathway of telomerase-negative regulation is the Rap1p pathway in yeast. Rap1p is bound throughout the telomeric sequence and interacts with two proteins, Rif1p and Rif2p (6, 7). The resulting complex is thought to prevent telomerase from accessing the telomeric DNA substrate by a yet unknown mechanism. Additional factors were shown to be involved in telomere length regulation. Tel1p and the yKu70p-yKu80p heterodimer act as positive regulators of telomerase (8-10). Tel1p is proposed to act by recruiting the MRX (Mer11͞Rad50͞Xrs2) complex (11). The yKu70p͞yKu80p heterodimer influences telomere length by protecting telomere ends from degradation. It also has additional functions in telomeric silencing (through recruiting Sir proteins to the telomeres), telomeric nuclear localization, and telomere replication timing (12-15). Cdc13p binds the telomeric single strand, recruits telomerase to the telomere, and prevents degradation (16,17). By these fu...