Abstract: We have previously demonstrated that genes within experimentally
characterized operons of Escherichia coli are conserved together in other
genomes more frequently than genes at the borders of transcription units. Here
we expand the analyses and show that, as the phylogenetic distance of the
genomes compared increases, the genes remaining together must belong to genes
associated into operons in other prokaryotes regardless of the operon
organization of the corresponding orthologous gene pair of E. coli. At the same
time, we show that the observed tendencies of genes within operons to keep very
short inter-genic distances in E. coli, is the same in any other prokaryote
whose genome is currently available. We also show the relationship between our
analyses of conservation and the inference of functional relationships from
genomic context.