Telomeres protect the ends of linear genomes, and the gradual loss of telomeres is associated with cellular ageing. Telomere protection involves the insertion of the 3′ overhang facilitated by telomere repeat binding factor 2 (TRF2) into telomeric DNA, forming t-loops. We present evidence suggesting that t-loops can also form at interstitial telomeric sequences in a TRF2-dependent manner, forming an interstitial t-loop (ITL). We demonstrate that TRF2 association with interstitial telomeric sequences is stabilised by co-localisation with A-type lamins (lamin A/C). We also find that lamin A/C interacts with TRF2 and that reduction in levels of lamin A/C or mutations in LMNA that cause an autosomal dominant premature ageing disorder —Hutchinson Gilford Progeria Syndrome (HGPS) — lead to reduced ITL formation and telomere loss. We propose that cellular and organismal ageing are intertwined through the effects of the interaction between TRF2 and lamin A/C on chromosome structure.

A phylogeny of marine Rhodophyta has been inferred by a number of methods from nucleotide sequences of nuclear genes encoding small subunit rRNA from 39 species in 15 orders. Sequence divergences are relatively large, especially among bangiophytes and even among congeners in this group. Subclass Bangiophycidae appears polyphyletic, encompassing at least three lineages, with Porphyridiales distributed between two of these. Subclass Florideophycidae is monophyletic, with Hlldenbrandiales, Corallinales, Ahnfeltiales, and a close association of Nemaliales, Acrochaetiales, and Palmariales forming the four deepest branches. Ceramiales may represent a convergence of vegetative and reproductive morphologies, as family Ceramiaceae is at best weakly related to the rest of the order, and one of its members appears to be allied to Gelidiales. Except for Gigartinales, for which more data are required, the other florideophyte orders appear distinct and taxonomically justified. A good correlation was observed with taxonomy based on pit-plug ultrastructure. Tests under maximumlikelihood and parsimony of alternative phylogenies based on structure and chemistry refuted suggestions that Acrochaetiales is the most primitive florideophyte order and that Gelidiales and Hildenbrandiales are sister groups.The Rhodophyta is a large, morphologically diverse assemblage of eukaryotes, with 2500-6000 species in about 680 genera (1). Although the division as a whole is well delimited (1, 2), its taxonomy at the levels of subclass and order has been unstable. Traditionally, two subclasses have been recognized, Bangiophycidae and Florideophycidae, with four and 14 orders, respectively. Recently, the former has been adjudged untenable (3-5) because it is not distinguished by synapomorphic characters. Alternatively, three new subclasses have been proposed to replace the Bangiophycidae and Florideophycidae on the basis of the degree of cellular transformation into spores (6). At the ordinal level (7), six new orders have been described since 1978 (8-12), and the large classical order Cryptonemiales has been subsumed into the similarly large Gigartinales (13), creating a heterogeneous assemblage of families that requires further resolution. Ordinal changes have arisen mainly from increasing appreciation of the significance of life-history variations and ultrastructure (5, 7, 9). However, taxonomic instability in Rhodophyta has also been ascribed to a lack of association with phylogenetic hypotheses, and attempts have been made (4, 6, 7) to infer phylogenetic relationships from morphological, anatomical, ultrastructural, life history, and chemical characters. Molecular sequences, particularly of nuclear genes encoding small subunit rRNA (SSU rDNAs) have proven useful in resolving phylogenetic relationships within other problematic groups (14-16 DNA Methods. DNA was extracted (18), and SSU rDNAs were amplified by using eukaryote-specific primers (19) as described (20). Amplification products were cloned into pUC and sequenced fully on both s...

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We have used molecular characteristics to darify the taxonomic status of three problematic gracilarioid algae, by comparison with existing data for the Gracilariaceae. Nucleotide sequences of nuclear-encoded 18S rDNA were determined for an unidentified species of Gracilariopsis from North Carolina, and two infertile strains of gracilarioid algae from Namibia, tentatively assigned to Gracilariopsis. The sequence from the North Carolinian alga was intermediate between those established previously for Gracilariopsis lemaneiformis and European Gracilariopsis sp., and represents a different, probably undescribed, species. Sequences from the Namibian plants were characteristic of Gracilaria, and very similar to those from Gracilaria verrucosa and two dosely related congeners. In parsimony, distance and maximum-likelihood analyses of these sequences and others already published for the Gracilariaceae, the North Carolinian Gracitariopsis sp. consistently grouped with its congeners, and the two Namibian strains with verrucosa-type species of Gracilaria. Restriction digestion of plastid DNA from the Namibian algae suggested that they were conspecific despite their different morphologies and agar characteristics. Moreover, the restriction patterns were nearly identical with those observed previously for Gracilaria verrucosa, and the Namibian strains are probably referable to this species.

SUMMARY We investigated phylogenetic relationships among red algae of the order Bangiales by analysis of sequences of the nuclear gene encoding cytosolic small‐subunit ribosomal RNA in Bangia atropurpurea (Roth) C. Ag. and eight samples representing seven species of Porphyra. The ssu‐rDNA range from 1818 to 1845 nucleotides in length, with guanosine plus cytosine ratios between 47.0% and 48.6%. A group IC1 intron occurs in the B atropurpurea ssu‐rDNAs at the same position as in P. spiralis var. amplifolia Oliveira Filho et Coll and several other eukaryote ssu‐rDNAs. The nine sequences form a stable monophyletic group upon phylogenetic analysis. The ssu‐rDNA from B. atropurpurea nests stably within the Porphyra group and is closely related to P. amplissima (Kjellm.) Setchell et Hus in Hus, making the genus Porphyra paraphyletic. No correlation is seen between phylogenetic position and number of cell layers in the Porphyra thallus. We discuss possible taxonomic and evolutionary implications of these observations.

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The genus Fucus L. is widely distributed through the cool temperate waters of the north Atlantic and north Pacific oceans. The very large number of sub-generic taxa (> 100) previously recognized was reduced by Powell (1963) to only 6 species. In his revision, Powell recognized F. distichus L. emend. Powell as the most variable of these. He classified the intra-specific variation in this species into 4 sub-species: F. distichus distichus, F. distichus anceps (Harv. et Ward ex. Carruthers) Powell, F. distichus evanescens (C.Ag) Powell and F. distichus edentatus (Pyl.) Powell. Because of reports that intermediate forms existed in Iceland (Jonsson, 1903) and the Faeröes (Börgesen, 1902), Powell (1957 a,b) decided to use sub-specific status rather than specific designation for these 4 taxa. However, within North America the 4 sub-species of F. distichus were often assigned specific rank (e.g. Taylor, 1957).