Multiple origins of a spider radiation in Hawaii.

The Hawaiian Islands are renowned for some of the most spectacular species radiations in the world. Most of these radiations have been attributed to single colonization events, although the evidence supporting monophyletic origins is often poorly resolved and/or ambiguous. Without a concrete understanding of the origins of species radiations, it is impossible to understand the phylogenetic pattern of species proliferation or the spectrum of morphological, ecological, and behavioral modifications attributable to a single colonist. In this study we examined the species radiation of the spider genus Tetragnatha in Hawaii. Unlike their mainland congeners, the Hawaiian Tetragnatha are extremely diverse in morphology, ecology, and behavior. We tested whether this diversity arose from a single or multiple colonization events. We coupled morphological (37 characters) and molecular (sequence from the 12S ribosomal subunit of mitochondrial DNA) approaches to assess the phylogenetic position of the Hawaiian Tetragnatha relative to continental congeners and to examine evidence for monophyly. We provide evidence that the Hawaiian Tetragnatha emanate from multiple origins. At least two independent species radiations, the "spiny-leg" clade and the web-building species Tetragnatha stelarobusta and Tetragnatha acuta, have arisen from one or more founder events. Two additional natural colonizations have resulted in the establishment of non-speciose lineages, as represented by Tetragnatha hawaiensis and Doryonychus raptor.

Normal Chlamydomonas nuclear gene structure on linkage group XIX.

The unusual Chlamydomonas linkage group XIX-called the uni linkage group for the uni mutants that lack one of the paired flagellae of wild-type cells--has been reported to be physically located exclusively at the basal bodies. To learn whether the structure of genes on this linkage group differs from the structure of nuclear genes in this organism, we determined the primary structure of a gene that maps to linkage group XIX. This analysis reveals the presence of nine intervening sequences; the nucleotides at exon/intron boundaries conform with nuclear gene intron junction sequences. Also typical for C. reinhardtii nuclear genes are the position and sequence of the putative polyadenylation signal. These findings suggest that transcripts from linkage group XIX are likely to be processed in the nucleus. The open reading frame, which displays weak but easily detected Chlamydomonas codon bias, potentially encodes a protein similar to a membrane anchor for cytoskeletal proteins. The observation that expression of this gene is regulated during interphase and in gametes is not consistent with the hypothesis that linkage group XIX may be expressed only during mitotic and meiotic processes.

The effects of elevated pH and high salt concentrations on tubulin.

The effects of incubating phosphocellulose-purified bovine tubulin at 4 degrees C in nucleotide-free buffers at alkaline pH or at high concentrations of NaCl, KCl, (NH4)2SO4, or NH4Cl have been studied. At pH greater than or equal to 7.5 or at NaCl concentrations greater than or equal to 0.7 M, tubulin releases bound nucleotides irreversibly and loses, with apparent first-order kinetics, the ability to assemble into microtubules. In 0.1 M 1,4-piperazinediethanesulfonic acid buffer, pH 6.9, in the presence of 1.3 M NH4Cl, tubulin undergoes more rapid loss of capacity to assemble than it does in NaCl and KCl, but 1.3 M (NH4)2SO4 causes no detectable change in tubulin after 1-h incubation. Incubation at high pH or at high neutral salt concentrations also causes an apparently irreversible change in the ultraviolet difference spectrum and in the sedimentation velocity profile of tubulin. At elevated salt concentrations a decrease of approximately 10% in the molar ellipticity within the wavelength range 220-260 nm is observed. The changes that occur during 1-h exposure to pH 8.0 can be completely prevented by including 1 mM guanosine 5'-triphosphate (GTP) or 4 M glycerol in the buffer, but those which occur at pH 9.0 cannot be prevented by these additions. In 1 M NaCl when the ratio of bound guanine nucleotide to tubulin reaches approximately 1.0, tubulin loses the abilities to assemble into microtubules and to bind colchicine. The rate of loss of nucleotide in 2 M NaCl is decreased in the presence of 1 mM GTP, and tubulin is protected almost completely from 1 M NaCl-induced loss of GTP (and retains the ability to exchange [3H]GTP as well) in the presence of bound colchicine. Investigators who anticipate exposing tubulin to buffers of elevated pH or high concentrations of chaotropic salts should be extremely cautious in interpreting the resulting data unless they can demonstrate that irreversible alteration of the protein has not occurred.

Release of exchangeably bound guanine nucleotides from tubulin in a magnesium-free buffer.

The number of moles of guanine nucleotides (denoted GXP), either guanosine 5'-triphosphate (GTP) or guanosine 5'-diphosphate (GDP), bound to a mole of phosphocellulose-purified tubulin after gel filtration into a variety of nucleotide-free buffers has been measured (H. B. Croom, J. J. Correia, and R. C. Williams, Jr., unpublished results). All buffers we have studied that promote reduction of the number of bound nucleotides to fewer than two per tubulin dimer also eventually cause irreversible loss of activity of the protein. However, in 0.1 M 1,4-piperazinediethanesulfonic acid (pH 6.9) and 2 mM dithioerythritol (with no Mg2+), tubulin rapidly releases approximately 0.4 mol of bound nucleotides during two successive gel filtrations requiring less than 0.5 h and regains the ability to polymerize when magnesium and GTP are immediately added to the buffer. No change in conformation detectable by circular dichroism or sedimentation velocity accompanies this reversible process. (Upon prolonged incubation in the buffer, however, tubulin undergoes irreversible changes according to apparent first-order kinetics with a half-life of approximately 8 h. These changes include the irreversible release of nucleotide, a loss of the ability to polymerize, and a decrease in molar ellipticity between 210 and 240 nm.) The nucleotide which is reversibly released in this buffer comes from that population which exchanges readily with [3H]GTP in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)