Transcription in Mycoplasma pneumoniae

Very little is understood of the structure of mycoplasma promoters, and thi s 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 weak consensus i n the -35 region. A high proportion of transcripts had heterogeneous 5'-end s and characterisation of the sequence of the 5'-ends of two transcripts es tablished that the heterogeneity was derived from initiation of transcripti on 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 transcr ipts lacked a 5' untranslated leader region that could contain a ribosomal binding site, Such leaderless transcripts are seen rarely-in other bacteria l species. Although the promoter regions for a number of members of lipopro tein multigene families were examined, no obvious-explanation for regulatio n of expression was apparent. Using the data from this study an improved ma trix 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.