Phylogenetic relatedness of selected ccrA and ccrB nucleotide sequences. The following genes were used: ccrA1 and ccrB1* from strain NCTC10442 [DDBJ:AB033763]; ccrA2 and ccrB2 from MRSA252 [EMBL:BX571856], MW2 [NCBI:NC_003923], SCCmec IIE [EMBL:AJ810120]; ccrA3 and ccrB3 of 85–3907 [DDBJ:AB047088]; ccrA4 and ccrB4* from HDE288 [GenBank:AF411935]; ccrA4 and ccrB4 of ATCC12228 [GeneBank:AE015929]; ccrC in WIS [DDBJ:AB121219]. The ccrB genes from NCTC10442 (ccrB1*) and HDE288 (ccrB4*) are truncated; for comparison we have reconstituted them by adding an adenine at the site of the frameshifts. The evolutionary relationships are shown by the length of the branches and the scale of the tree indicates the number of nucleotide substitutions per 100 bases. Alignment was done using ClustalW and tree constructed with Multalign, Lasergene 6.0. Type 4 ccrA genes are framed in red and and type 4 ccrB genes in green.