project has benefited from parallel efforts to sequence the genome of M. avium. Preliminary reports from the Map sequencing project demonstrate overall 99 percent sequence identity between Map and MAC. The Map genome size, at 5.5 million base-pairs, appears larger than that of M. tuberculosis and M. avium. Twenty-one unique genes had been identified as of January 2002 and it is projected that a total of about 50 will be identified when the project is complete. Among these is a new gene cluster without homology to any known genes at both the genome and possibly at the protein level. Preliminary expression studies have been started comparing expressed genes from culture vs. organisms cultivated in an immortalized macrophage cell line. Several repetitive elements have also been identified in addition to IS900 and IS1311. As might be expected, there are variations in sequence length between different copies of IS900 suggesting heterogeneity in this insertion element. This may be of value in more refined studies of strain relatedness.
Results of the gene-sequencing project have the promise to provide diagnostic reagents with improved sensitivity and specificity. Expression libraries may help to identify unique antigens that can be used in developing serological assays and tests of cell-mediated immunity. They may also provide the foundation for rational vaccine development. These diagnostic approaches may additionally provide adequate specificity and sensitivity to assess definitively the role of Map in human disease.