Schematic representation of mutant virus genomes. The top line represents the K181⁺ strain MCMV genome¹⁶  with nucleotide numbers (GenBank accession number U68299). The MCMV ie1/ie2/ie3 transcriptional enhancer (hatched box) and transcripts (solid arrows) encoded by the wild-type viruses also are shown in the expanded region. Open boxes depict the positions of ORFs m131 and m129 that encode MCK-2.¹²  The mutations introduced into recombinant viruses RM461,¹⁶  RM427⁺,¹⁴  RM4503,⁴⁶  and RM4511¹¹  are depicted below the transcripts. The lacZ insertion in RM461 or RM427⁺ (open box) and the EGFP-puro insertion in RM4503 or RM4511 (open box) are depicted below the map. Two nucleotide point mutations were introduced into RM4511 to alter the conserved CC chemokine motif in MCK-2 (C₂₇R and C₂₈G; 14).