eLife assessment
This useful study seeks to address the importance of physical interaction between proteins in higher-order complexes for covariation of evolutionary rates at different sites in these interacting proteins. Following up on a previous analysis with a smaller dataset, the authors provide solid evidence that the exact contribution of physical interactions, if any, remains difficult to quantify. A weakness of the study is that alternative hypotheses, specifically the importance of similar expression levels and patterns of genes that encode interacting proteins -- for which there is already substantial evidence in the literature -- are not sufficiently considered. The work will be of relevance to anyone interested in protein evolution.