 Many of the clusters span sufficient diversity that the genomes warrant division into subclusters (Figure 1).There is also considerable range in overall guanine plus cytosine content (GC%), from 50.3% to 70%, with an average of 64% ("M. smegmatis" is 67.3%).Thus, phage GC% does not necessarily match that of its host, and the consequent mismatch of codon usage profiles does not appear to be detrimental.