Technology

Scanometric DNA detection with nanoparticle probes. Taton, T. A. et al. Science 289 , 1757–1760 (2000). [ Pubmed]

In microarray experiments, the DNA hybridizing to the chip is usually labelled with a fluorescent dye. These authors have labelled the DNA with a gold nanoparticle. The specificity of the hybridization reaction allows single-base mismatches to be detected and the sensitivity of detection is increased by two orders of magnitude relative to a fluorescent label. The method could have important applications such as single nucleotide polymorphism screening in the analysis of human disease.

Human genetics

An SNP map of the human genome generated by reduced representation shotgun sequencing. Altshuler, D. et al. Nature 407 , 513–516 (2000).[ abstract] [ PubMed]

An SNP map of human chromosome 22. Mullikin, J. C. et al. Nature 407 , 516–520 (2000). [ abstract] [ PubMed]

Single nucleotide polymorphisms (SNPs) are the markers of choice for mapping complex disease loci. There is some debate about how many will be needed, but these two papers report the first fruits of the SNP consortium — an academic–industrial collaboration aiming to identify around 300,000 SNPs covering the human genome. The papers present alternative approaches to SNP identification and suggest that the SNP consortium will easily exceed its goal.

Evolution

Mutators and sex in bacteria: Conflict between adaptive strategies.  Tenaillon, O. et al. Proc. Natl Acad. Sci. USA 97 , 10465–10470 (2000). [ PubMed]

Mutator alleles, which increase the mutation rate, can spread in an asexual population because they remain associated with the favourable alleles that they generate. Although mutator strains of bacteria would be expected to reach a very high frequency during the fixation of advantageous alleles, this does not occur. Using simulation models, the authors show that even rare genetic exchanges, such as occur by transduction and conjugation, are sufficient to reduce the selective spread of mutator strains.

Yeast genetics

swi1 and swi3 perform imprinting, pausing and termination of DNA replication in S. pombe. Dalgaard, J. Z. & Klar, A. J. S. Cell 102 , 745–751 (2000). [ contents page] [ PubMed]

In mating-type switching in S. pombe, DNA at the mat1 locus is replaced by DNA from one of two silent mat loci by recombination. This occurs by the introduction of a chromosomal imprint at mat1 during the S phase — an event that is sensitive to the direction of DNA replication. This paper reports the roles of swi1 and swi3 in this process and shows that they pause DNA replication to allow the chromosomal imprint to be established and terminate replication to block the entry of a replication fork from the opposite direction.