Nucleotide sequence of the 19 kDa antigen gene from Mycobacterium tuberculosis.

The 19 kilodalton (kDa.) antigen of Mycobacterium tuberculosis is one of several serologically immunodominant antigens found in this bacillus (1,2). We have determined independently the nucleotide sequence of the gene encoding the 19 kDa. antigen (Fig. 1) from the DNA inserts of two Xgtl I clones (Y3147 and Y3293 - sequenced by R. Lathigra) isolated from the M. tuberculosis genomic DNA library (2). The putative gene encodes a 159 amino acid protein with a calculated molecular weight of 15.1 kDa. This size is in agreement with a relative mobility of 16-17 kDa. observed on Western blots when this gene is expressed in E. coli (K. Ashbridge, unpublished observation). Interestingly, GTG appears to serve as the initiation codon for this protein, a feature not previously described for a mycobacterial gene. The inferred protein sequence of the 19 kDa. antigen reveals an curious structure, with 15 double anmino acid repeats present in the initial two-thirds of the molecule. 245