Classification of sequencing reads. Sequencing reads of at least 18 nucleotides in length were blasted against the C. pneumonia CWL-029 genome. (a) The fraction of sequences that could be mapped to the Chlamydia genome is given for each library. Sequence reads shorter than 17 nucleotides were not considered for BLAST search. (b) The distribution of sequence reads among the different classes of RNA is shown for each library. Nt, nucleotides; TEX, terminator exonuclease.