M.bovis (strains ATCC BAA-935 / AF2122/97 and BCG / Pasteur 1173P2) and M.marinum (strain ATCC BAA-535 / M) have a single fused pks15/1 ORF, but M.tuberculosis (strains ATCC 25618 / H37Rv and CDC 1551 / Oshkosh) have 2 separate ORFs. This is due to the natural deletion of a single base, a guanine, that causes a frameshift and thus the two ORFs, pks15 and pks1, instead of pks15/1. This frameshift led to the inactivation of Pks15/1, which in turn caused the inability of these strains to elongate the putative p-hydroxybenzoic acid precursor and thus to produce phenolphthiocerol derivatives.