Transcription in Mycoplasma pneumoniae

Very little is understood of the structure of mycoplasma promoters, and this limits interpretation of genomic sequence data in these species. In this study the transcriptional start points of 22 genes of Mycoplasma pneumoniae were identified and the regions 5′ to the start point compared. Although a strong consensus –10 region could be seen, there was only a weak consensus in the –35 region. A high proportion of transcripts had heterogeneous 5′-ends and characterisation of the sequence of the 5′-ends of two transcripts established that the heterogeneity was derived from initiation of transcription at reduced levels between 1 and 4 bases 5′ to the major starting point. In addition to this apparently unique feature, a high proportion of transcripts lacked a 5′ untranslated leader region that could contain a ribosomal binding site. Such leaderless transcripts are seen rarely in other bacterial species. Although the promoter regions for a number of members of lipoprotein multigene families were examined, no obvious explanation for regulation of expression was apparent. Using the data from this study an improved matrix for prediction of M.pneumoniae promoters was derived. Application of this matrix to the sequences immediately 3′ and 5′ to each predicted start codon in the genome suggested that most M.pneumoniae transcriptional start points were likely to occur between 5 and 30 bases 5′ to the start codon.