Location, location, location

Expression of a gene is in a sense a bit like purchasing a new home - the value is strongly dependent on location. This value is context-dependent: it depends on who your neighbors are and also on the larger geographical picture. Two recent studies have analyzed DNA topology and chromatin structure on a genome-wide scale in Escherichia coli [1, 2]. Both show that an important factor in determining transcription profiles - when and to what extent a gene is expressed - is the location of the gene within the context of the E. coli K-12 chromosome. Whereas this is old news for those who are interested mainly in eukaryotic chromosomes, it is an important concept that has often been overlooked (in our opinion) in bacterial transcriptomics. In eukaryotes, it is well known that there are two types of chromatin: heterochromatin, which remains condensed for the most part throughout the cell cycle and contains few genes, and euchromatin, which, on the other hand, contains gene-rich regions and in some cases clusters of highly expressed genes.