The atomic structure of the stable tetramerization domain of the measles virus phosphoprotein shows a tight four-stranded coiled coil. Although at first sight similar to the tetramerization domain of the Sendai virus phosphoprotein, which has a hydrophilic interface, the measles virus domain has kinked helices that have a strongly hydrophobic interface and it lacks the additional N-terminal three helical bundles linking the long helices.