To characterize the genetic determinants of resistance to antituberculosis drugs, we performed a genome-wide association study (GWAS) of 6,465 Mycobacterium tuberculosis clinical isolates from more than 30 countries. A GWAS approach within a mixed-regression framework was followed by a phylogenetics-based test for independent mutations. In addition to mutations in established and recently described resistance-associated genes, novel mutations were discovered for resistance to cycloserine, ethionamide and para-aminosalicylic acid. The capacity to detect mutations associated with resistance to ethionamide, pyrazinamide, capreomycin, cycloserine and para-aminosalicylic acid was enhanced by inclusion of insertions and deletions. Odds ratios for mutations within candidate genes were found to reflect levels of resistance. New epistatic relationships between candidate drug-resistance-associated genes were identified. Findings also suggest the involvement of efflux pumps (drrA and Rv2688c) in the emergence of resistance. This study will inform the design of new diagnostic tests and expedite the investigation of resistance and compensatory epistatic mechanisms.

Three vitellogenin genes from the free-living nematode Caenorhabditis elegans have previously been characterized at the molecular level. In order to study evolutionary relationships within this poorly understood taxon, we have cloned a vitellogenin gene, CEW1-vit-6, from a distantly related species belonging to the same family as C. elegans. Screening of a genomic library with a probe to total poly(A+) RNA yielded three clones that hybridized more intensely than all others, and all three corresponded to a single gene homologous to C. elegans vit-6. Comparison of CEW1-vit-6 with Ce-vit-6 reveals both strong similarities and surprising differences. Life Ce-vit-6, the gene is about 5 kb long and contains four unusually small introns (38-41 nt), but only one interrupts the gene at the same location as a Ce-vit-6 intron. The promoter region contains five matches to Vitellogenin Promoter Element 1 (VPE1) and no matches to VPE2, both previously shown to be required for vit gene transcription in C. elegans. Codon usage is in general similar to that of the Ce-vit genes, but a few codon biases are quite different. Alignment of the CEW1-vit-6 protein with Ce-vit-6 and Ce-vit-2 products suggests the existence of two domains which have evolved at different rates. Sequence comparison shows that nematode vitellogenins are much more closely related to vertebrate than to insect vitellogenins.

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