Tag Archives: genes

Approaching 100% coverage for GO assignments in S.pombe

A paper by Martin Aslett and Val Wood indicate that the fission yeast community is approaching 100% coverage of a GO annotation for every gene in the S. pombe genome. Only Ashbya gossypii has a smaller genome in the fungi (see a recent paper on Ashbya annotation database) and doesn’t yet have complete GO coverage. This is quite remarkable and a great dataset for studies in S. pombe and all fungi.

S. pombe taken from Paul Young’s site

My quick predictions of genes a closely related species, S. japonicus, has more than twice as many genes as S. pombe (but be over-prediction by ab initio predictors). Taken in comparison to many other fungi, S. pombe represents a streamlined and reduced genome which probably occured indepdently from reduction in the Hemiascomycetes.

Whole genome tiling arrays

A recent paper describes the discovery of 9 new introns in Saccharomyces cerevisiae by Ron Davis’s group at Stanford, using high density tiling arrays from Affymetrix. The arrays are designed for both strands allow the detection of transcripts transcribed from both strands. The arrays were also put to work by the Davis and Steinmetz labs to create a high density map of transcription in yeast and for polymorphism mapping from the Kruglyak lab.

PNAS Yeast Transcriptional map

Whole genome tiling arrays have also been employed in other fungi. For example, Anita Sil’s group at UCSF constructed a random tiling array for Histoplasma capsulatum and used it to identify genes responding to reactive nitrogen species. A similar approach was used in Cryptococcus neoformans to investigate temperature regulated genes using random sequencing clones.

As the technology has become cheaper, it may become sensible to use a tiling array to detect transcripts rather than ESTs when attempting to annotate a genome. In the Histoplasma work transcriptional units could be identified from hybridization alone. Some of the algorithms will need some work to correct incorporate this information, and the sensitivity and density of the array will influence this. These techniques can be part of a resequencing approaches or fast genotyping progeny from QTL experiments when the sequence from both parents is known (or at least enough of the polymorphims for the genetic map).

What is superior about the current Affymetrix yeast tiling array is the inclusion of both strands. This allows detection of transcripts from both strands. Several anti-sense transcripts in yeast have been discovered recently including in the IME4 locus through more classical approaches, but perhaps many more await discovery with high resolution transcriptional data from whole genome tiling arrays.