USE OF A MYCOBACTERIUM-TUBERCULOSIS H37RV BACTERIAL ARTIFICIAL CHROMOSOME LIBRARY FOR GENOME MAPPING, SEQUENCING, AND COMPARATIVE GENOMICS

The bacterial artificial chromosome (BAC) cloning system is capable of stably propagating large, complex DNA inserts in Escherichia coli, As part of the Mycobacterium tuberculosis H37Rv genome sequencing projec t, a BAC library was constructed in the pBeloBAC11 vector and used for genome mapping, confirmation of sequence assembly, and sequencing. Th e library contains about 5,000 BAC clones, with inserts ranging in siz e from 25 to 104 kb, representing theoretically a 70-fold coverage of the M. tuberculosis genome (4.4 Mb), A total of 840 sequences from the T7 and SP6 termini of 420 BACs were determined and compared to those of a partial genomic database, These sequences showed excellent correl ation between the estimated sizes and positions of the BAC clones and the sizes and positions of previously sequenced cosmids and the result ing contigs, Many BAC clones represent linking clones between sequence d cosmids, allowing full coverage of the H37Rv chromosome, and they ar e now being shotgun sequenced in the framework of the H37Rv sequencing project. Also, no chimeric, deleted, or rearranged BAC clones were de tected, which was of major importance for the correct mapping and asse mbly of the H37Rv sequence, The minimal overlapping set contains 68 un ique BAC clones and spans the whole H37Rv chromosome with the exceptio n of a single gap of similar to 150 kb, As a postgenomic application, the canonical BAC set was used in a comparative study to reveal chromo somal polymorphisms between M. tuberculosis, M. bovis, and M. bovis BC G Pasteur, and a novel 12.7-kb segment present in M. tuberculosis but absent from M, bovis and M. bovis BCG was characterized. This region c ontains a set of genes whose products show low similarity to proteins involved in polysaccharide biosynthesis. The H37Rv BAC library therefo re provides us with a powerful tool both for the generation and confir mation of sequence data as well as for comparative genomics and other postgenomic applications, It represents a major resource for present a nd future M. tuberculosis research projects.