Transcription regulation, a key step in the control of gene expression, has been the focus of several large-scale studies; however, little attention has been given to its relationship with the chromosomal arrangement of transcription units. We studied this relationship systematically in Escherichia coli and Saccharomyces cerevisiae using network analysis methods. Our analysis reveals links between transcription regulation and chromosomal organization, suggesting that in both organisms transcription regulation has shaped the organization of transcription units on the chromosome. Differences found between the organisms reflect the inherent differences in transcription regulation between prokaryotes and eukaryotes.