Relatedness of MSG genes adjacent to the UCS locus in the population of P. carinii used to prepare inocula. Inserts in 36 plasmids carrying UCS-MSG junctions amplified from the input population were sequenced. Twenty-seven different sequences were present. Five sequences were present in more than one plasmid. These are numbered, e.g., 1.1 and 1.2. The sequences were aligned by pairwise comparisons, and percent identities were calculated. These are displayed in the dendrogram. The horizontal branch lengths represent divergence, and the bar above the dendrogram shows percent identity. To illustrate, sequences and 17 and 18 differed by ∼17%. Sequence 13 matched that predominant in inoculated rats 271 and 272. Sequence 23 matched 13, which matched that predominant in inoculated rats 273 and 274. The sequence in plasmids 15.1, 15.2, and 15.3 was the same as that seen in inoculated rat 267.