Mouse models of cancer are primarily soft tissue sarcomas and lymphomas, whereas 90% of human cancers are epithelial in origin. In the August 10 Nature, Artandi et al. suggest that the difference arises from higher levels of telomerase (the enzyme that adds a protective cap on the end of chromosomes) in mice (Nature 2000, 406:641-645). When the researchers combine a mouse telomerase knockout with a mutation in the tumor suppressor p53, non-reciprocal translocations appear, followed by epithelial

Cohesins , the proteins that are thought to anchor sister chromatids to one another before anaphase, must be present during DNA replication if cohesion is to be established. In the 4 August Science Wang et al . provide a possible link between replication and cohesion (Science 2000, 289 :774-779). They describe an essential DNA polymerase in budding yeast that both has polymerase activity and is required for sister chromatid cohesion. They suggest that the replication fork m

In the August Nature Genetics , two groups report on their ongoing large-scale projects to produce mouse mutants using the chemical mutagen ethylnitrosourea. An English and French group have screened over 26,000 F1 progeny for dominant defects in growth and development, and a subset of these for defects in neural and behavioral function and blood chemistry (Nolan et al ., Nat. Genet . 2000, 25 :440-443). Their results are cataloged in Mutabase . Approximately half of the

DNA shuffling (also called molecular breeding) generates variation by random fragmentation of a cloned gene followed by reassembly of the fragments in a self-priming polymerase reaction. The result is a recombination of overlapping fragments that have different mutations or come from different, naturally occurring homologous genes. In the August Nature Genetics Soong et al apply this technique to a pool of six different murine leukemia virus envelope sequences to derive a new virus that can,

DNA microarray analysis of metastatic cells reveals a new player, and an expression profile characteristic of reduced motility and invasive ability.

suggests that the bacterium's second chromosome may have started life as a megaplasmid.

An RNA polymerase crystal structure and crosslinking data are combined to give clues about how transcription works.

If synergistic epistasis occurs, each mutation added to a genome has a greater deleterious effect than preceding mutations. Without this effect it is difficult to explain how small populations can survive in the face of genetic drift, or how larger populations can survive a high mutation rate. In the 27 July Nature Peck and Waxman use a mathematical model to deduce that competition in small groups does, indeed, lead to synergistic epistasis (Nature 2000, 406:399-404). This competition also produ

BRCA1 is a tumor-suppressor gene linked to familial breast and ovarian cancers. In the July 21 Cell, Bochar et al. find that the predominant BRCA1-containing complex in human cells is the SWI/SNF-related chromatin remodeling complex (Cell 2000, 102:257-265). This may explain the multitude of properties that have been ascribed to BRCA1, including effects on transcription, DNA repair, and cell-cycle checkpoints. Mutations in SNF5, another subunit of the SWI/SNF complex, have been shown to result i

BAF, a cellular protein that prevents virus autointegration, may normally function in chromosome condensation.

Mobile group II intron RNAs insert directly into DNA target sites before being reverse-transcribed by an intron-encoded protein. Target site recognition involves base-pairing between the RNA and DNA, and interactions between flanking DNA and the intron-encoded protein. In the 21 July Science, Guo et al use an Escherichia coli-based selection procedure and randomized intron sequences to derive group II introns capable of inserting into alternative target sites (Science 2000, 89:452-457). One of t

Were the Pacific islands of Polynesia colonized by people migrating from Taiwan or Melanesia? Su et al suggest in the July 18 Proceedings of the National Academy of Sciences that neither theory is correct, and that southeast Asia may have been the starting-off point (Proc. Natl. Acad. Sci. USA 2000, 97:8225-8228). They base their claims on haplotypes from the nonrecombining portion of the Y chromosome. Only one Polynesian haplotype is shared with the Taiwanese, whereas nine of ten Pacific island