The multiprotein complexes that mediate replication, transcription and homologous recombination in eukaryotic cells face many of the same molecular challenges. These include the recognition of DNA sites embedded in large chromatinized genomes, the denaturation of duplex DNA, and partial dissociation and reassociation at different stages of the catalytic cycle. Therefore, it is not surprising that several steps in the respective catalytic cycles are strikingly similar at the DNA level and may proceed by similar mechanisms. Some of these relationships are reviewed here. It is argued that speculation based on such 'crosspathway' comparisons may be a valuable paradigm for the design of new experiments.