Two eukaryotic DNA polymerases act sequentially to repair DNA lesions.

An exon, the basic unit of DNA that gets shuffled around during evolution, has an average coding capacity of 40 amino acids, or roughly half of a small folded protein domain. Exon exchange between homologous proteins can lead to slightly altered proteins, but in the August 29 Proceedings of the National Academy of Sciences Riechmann and Winter ask whether shuffling between unrelated sequences can generate new folds (Proc Natl Acad Sci USA 2000, 97:10068-10073). Their starting material is DNA enc

, the bug responsible for most cystic fibrosis deaths, reveals lots of pumps and lots of regulation.

Female Trinidadian guppies often mate with multiple males, because the resultant offspring show substantially increased fitness.

With sequence information in hand, the search for regulatory sites in promoters can be done by computers rather than cloning. But the primary tools for analysis, multiple-alignment algorithms, can only handle a small amount of sequence data. In the August 29 Proceedings of the National Academy of Sciences, Bussemaker et al. introduce an alternative algorithm that they dub 'MobyDick' (Proc Nat Acad Sci USA 2000, 97: 10096-10100). MobyDick treats DNA sequence as text in which allthewordshavebeenru

In the 18 August Science St. Croix et al. present an expression analysis of endothelial cells from blood vessels of normal and malignant colorectal tissue (Science 2000, 289:1197-1202). After developing a method for purifying these scarce cells, they use serial analysis of gene expression (SAGE) to identify a host of new pan-endothelial markers that are not expressed in other tissues. Additionally, 46 SAGE tags are elevated tenfold or more specifically in tumor endothelium, and at least 7 of the

DNA microarrays are normally used to detect variation in mRNA abundance. But in the August 15 Proceedings of the National Academy of Sciences Khodursky et al. use the arrays to track the progress of replication forks in Escherichia coli (Proc Natl Acad Sci USA 2000, 97:9419-9424). In a bacterial culture that is replicating synchronously, genomic DNA from replicated regions gives a stronger array signal than unreplicated DNA. Khodursky et al. use this signal variation to show that normal replicat

In the 17 August Nature Perou et al. present a DNA microarray analysis of 65 human breast tumor specimens from 42 different individuals (Nature 2000, 406:747-752). Of the 8,102 genes analyzed, 1,753 varied in abundance at least fourfold in at least three samples. These genes could be clustered into groups that correlated with mitotic index, regulation of the interferon pathway, and the relative abundance of endothelial cells, stromal cells, adipose cells, B or T cells and macrophages. Expression

On 2 July 2000, a small black piglet was delivered by a white sow. Xena's dark color was a clue that she was not the warrior princess whose name she bears but the product of the first successful pig cloning from fetal cells. As reported in the 18 August Science, this cloning adds to reports of cloned sheep, cattle, and goats (Onishi et al, Science 2000, 289:1188-1190). Xena was produced using a technique developed in mice in which a nucleus from a somatic cell is microinjected into an enucleated

A series of narrow-pH-range overloaded 2D gels, processed using sensitive silver-staining, yields enough spots that the gels could, theoretically, be surveying virtually all of the proteins of budding yeast. But in the August 15 Proceedings of the National Academy of Sciences, Gygi et al. report that proteomics proponents may have been fooling themselves (Proc Natl Acad Sci USA 2000, 97:9390-9395). Gygi et al. select a random region of one such gel and analyze all the visible spots. The genes co

Sea urchins are popular in developmental biology research thanks to their well defined embryology, the ease of gene transfer into eggs, and the abundance of eggs for biochemical work. Now the sea urchin genome project is off to a start with sequence from the ends of 76,020 bacterial artificial chromosome (BAC) recombinants. In the August 15 Proceedings of the National Academy of Sciences, Cameron et al. report that these sequence tag connectors (STCs) occur at an average of 10 kb apart in the s

In the 10 August Nature, Burch and Chao find that two populations of an RNA virus, derived from a single ancestral phage, repeatedly evolve towards different fitness maxima (Nature 2000, 406:625-628). The average fitness of one of the final phage populations is actually lower than that of the starting clone, suggesting that the original individual was at the peak of a local maximum of fitness. The existence of these different and non-overlapping solutions to maximizing fitness suggests that the