800 oscillations per cycle

Sequencing of the yeast Saccharomyces cerevisiae genome finished just one year ago, but post-genomic analyses are in full swing. The first major operation has been to survey the 6000 or so genes to see which of them show cell-cycle-regulated expression. The answer is at least 400 and perhaps as many as 800. To arrive at these numbers, mRNA was extracted from synchronized yeast cells throughout the cell cycle and analysed by DNA microarray technology. The two studies to date use rather different methods and on the face of it seem to give very different results; the first study1xA genome-wide transcriptional analysis of the mitotic cell cycle. Cho, R.J. et al. Mol. Cell. 1998; 2: 65–73Abstract | Full Text | Full Text PDF | PubMedSee all References1 failed to find almost 500 genes identified in the second, more sensitive, analysis2xComprehensive identification of cell cycle-regulated genes of the yeast Saccharomyces cerevisiae by microarray hybridization. Spellman, P.T. et al. Mol. Biol. Cell. 1998; 9: 3273–3297Crossref | PubMedSee all References2 (and found instead 100 others), but, looking on the bright side, there is agreement on 300 genes. Most of the genes show up for obvious reasons, being involved in controlling the cell cycle itself, in DNA replication and repair, and in mitosis, for example. However, there are surprises too, with genes involved in regulating nutrition cropping up, for instance. This suggests that both ‘cause’ and ‘effect’ messages are within the reach of these genome chips.Given the genome sequence, substantial promoter analysis is possible. Most of the identified genes do, happily, have target sites for known cell-cycle transcription factors. Indeed, through this analysis, it has been possible to refine the binding sites for certain of these factors. Other identified genes do not have recognizable sites; thus, it is not so easy presently to understand their oscillatory behaviour. However, the data generated by these studies provide a very valuable resource for further analyses, and also might act as a guide for the behaviour of human homologues of many of these genes.