Researchers hoping to decipher the first complete genome sequence of a plant fear the lengthy clusters of repeated transposon sequences present in many plant genomes. But in the July issue of Genome Research, Mao et al. report promising news for the international consortium tackling the rice genome (Genome Res. 2000, 10:982-990). After sequencing 73,000 DNA fragments distributed through the rice genome (a total of nearly 50 Mb), Mao et al. find that less than 10% of the sequences contain transpo

A compendium of expression profiles from mutant yeast strains allows function to be attributed to uncharacterized genes and leads to the identification of a drug target.

Mad2p is a budding yeast protein that helps to delay progression through mitosis until errors in chromosome attachment to the mitotic spindle are corrected. In the 14 July Science Shonn et al. find that this spindle checkpoint is also required during meiosis (Science 2000, 289:300-303). Cells without Mad2p show increased chromosome segregation errors during budding yeast meiosis I, when homologs separate, but appear normal during meiosis II, when sister chromatids separate. Meiosis I may fare le

In the 13 July Nature a Brazilian sequencing consortium reports the first public sequence of a free-living plant pathogen (Nature 2000, 406:151-159). The bacterium, Xyella fastidiosa, grows in the water-conducting xylem of citrus plants and causes chlorosis (yellowing) and premature production of small, tough fruit. The sequence reveals a metabolism focussed on carbohydrate consumption and extensive biosynthetic capability to compensate for the scarcity of biological small molecules in the xylem

The rate at which electrons and holes move along DNA is sufficient to prevent strand-cleavage reactions, but too slow to make DNA a useful molecular wire.

Depletion of stratospheric ozone increases the amount of ultraviolet-B (UV-B) irradiation experienced on Earth. Now Ries et al. report in the 6 July Nature that increased UV-B exposure can reduce the genomic stability of plants (Nature 2000, 406:98-101). They use a reporter gene inserted as a tandem or inverted repeat as a probe to detect 1.7-fold to 14-fold increases in homologous recombination after increasing UV-B levels. The plant germline is protected from UV-B for much of its life, and yet

The function of an uncharacterized gene can sometimes be determined by mutating the gene and using a phenotypic assay But sometimes a convenient phenotype does not exist for a given cellular function. Hughes et al. suggest in the July 7 Cell that expression profiles can be used instead (Cell 2000, 102:109-126). Rather than measuring expression profiles as conditions change (e.g., at different points in the cell cycle, Hughes et al. keep the culture conditions constant and measure the profiles of

The transcription factors TFIID and SAGA are multi-subunit complexes involved in RNA polymerase II transcription. In the 8 June Nature Lee et al. use oligonucleotide arrays to analyze the relative requirement for the two complexes in yeast (Nature 2000, 405:701-704). Expression of about 70% of yeast genes requires one or more of the subunits shared between TFIID and SAGA, although individual subunits were required to varying extents, and no single subunit was required to the same extent as RNA p

According to a new phylogenetic analysis, the subtype of HIV that causes the majority of AIDS cases started diverging around 1931. The results of the analysis, which was conducted on the Los Alamos supercomputer 'Nirvana' using sequences from 159 envelope genes, are reported in the 9 June Science (Korber et al., Science 2000, 288:1789-1796). The computation used a molecular clock model presuming a constant rate of sequence change, but similar results were obtained with models that allowed change

In the 2 June Science, Phillips et al announce the creation of the Stem Cell Database (SCDb), an annotated collection of genes expressed in hematopoietic stem cells (Science 2000, 288:1635-1640). Most of the data are based on the sequencing of 5735 clones from a subtracted stem cell library, representing at least half of the library's complexity. The SCDb reveals clues to stem cell biology, such as the coincidence of semaphorins and their ligands, suggesting that these molecules are important fo

Differentiation of embryonic stem (ES) cells, which are originally totipotent, puts increasing restrictions on the final fates that a cell can achieve. This simple idea was upset last year when neural stem cells were shown to produce blood cells in irradiated adult mice. In the 2 June issue of Science, Clarke et al. show that neural stem cells injected into embryos can generate a wide variety of tissues including cells in the central nervous system, heart, liver, and intestine (Science 2000, 288

The stochastic nature of every chemical event in the cell generates noise that can lead to large fluctuations in protein and mRNA levels. Autoregulatory negative feedback loops in gene circuits have been proposed, but never shown, to be one way of limiting this variation. With a simple experiment, in the 1 June Nature Becskei and Serrano demonstrate that negative feedback can decrease the inherent variability of gene expression more than threefold. They direct expression of a hybrid protein (gre