Sequence analysis of IS900 of several M.paratuberculosis strains from different origin revealed the presence of an additional 'GC' pair at position 36, when compared with the published nucleotide sequence data. As a consequence, transcription of the IS900 element into mRNA results into a putative open reading frame ORF2 or hed, with a termination codon (UAA ) just prior to the 3í end of the insertion element. The transcriptional organisation is therefore identical to homologous insertion elements like IS901/902 and IS116 of M. avium and S. clavuligerus respectively. In other words: using the promotor sequence provided at the insertion site by the host for the expression of ORF2 and providing itself a ribosomal binding site to the open reading frame present in the interrupted operon at the insertion site. Therefore, insertion of the IS900-element is not likely to disrupt the expression of genes present at this site. In addition, detection of M. paratuberculosis by PCR using primers based on the published sequence including this error (eg. primer p90) will be severely hampered, by affecting both the specificity and sensibility of the reaction as shown by quantitative PCR based on Taqman technology.