The ubiquitin linkage preference by the SNL domain of SidC. (A) In vitro ubiquitination assays using E1, UbcH7, SNL domain, and a set of ubiquitin mutants with a single K-to-R mutation. K0 represents the ubiquitin mutant carrying all seven K-to-R to mutations. (B) In vitro ubiquitination assays using E1, UbcH7, SNL domain, and a set of ubiquitin containing a single native lysine with six K-to-R mutations.