Transcript analysis of 1003 novel yeast genes using high-throughput northern hybridizations

The expression of 1008 open reading frames (ORFs) from the yeast Saccharomy ces cerevisiae has been examined under eight different physiological condit ions, using classical northern analysis. These northern data have been comp ared with publicly available data from a microarray analysis of the diauxic transition in S, cerevisiae. The results demonstrate the importance of com paring biologically equivalent situations and of the standardization of dat a normalization procedures. We have also used our northern data to identify co-regulated gene clusters and define the putative target sites of transcr iptional activators responsible for their control. Clusters containing gene s of known function identify target sites of known activators. In contrast, clusters comprised solely of genes of unknown function usually define nove l putative target sites. Finally, we have examined possible global controls on gene expression. It was discovered that ORFs that are highly expressed following a nutritional upshift tend to employ favoured codons, whereas tho se overexpressed in starvation conditions do not, These results are interpr eted in terms of a model in which competition between mRNA molecules for tr anslational capacity selects for codons translated by abundant tRNAs.