FIG. 3. Phylogenetic tree of selected members of the PE family. The tree was deduced from a multiple sequence alignment and relational analysis and proteins are referred to by the cosmid identifiers used throughout the project. Note the tight clustering of the polymorphic GC-rich sequence (PGRS) members, MTCY06H11_16c through MTCY1A10-19, compared to the other PE proteins, MTCY98_0011c through MTCI5-25c, which have unique sequences in the C-terminal domain.

MPTR-coding sequences have been detected in Mycobacterium gordonae, Mycobacterium kansasii and Mycobacterium marinum (Poulet & Cole 1995a,b, Ross et al 1992), and in Mycobacterium asiaticum, Mycobacteriumgastri and Mycobacterium s^ulgai, respectively (Hermans et al 1992). On examination of the protein database from the extensively sequenced Mycobacterium leprae, no PGRS- or MPTR-related polypeptides were detected, but some proteins belonging to the non-MPTR subgroup of the PPE family were found. These include the serine-rich antigen described by Stoker et al (Vega-Lopez et al 1993) who identified the corresponding gene in an expression library using serum from lepromatous leprosy patients. Immunological studies with a recombinant form of the protein showed that sera from the majority of lepromatous and tuberculoid patients recognized this protein, suggesting that it corresponds to a major antigen.

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