Prediction of rho-independent transcriptional terminators in Escherichia coli

A new algorithm called RNAMotif containing RNA structure and sequence const raints and a thermodynamic scoring system was used to search for intrinsic rho-independent terminators in the Escherichia coli K-12 genome. We identif ied all 135 reported terminators and 940 putative terminator sequences begi nning no more than 60 nt away from the X-end of the annotated transcription units (TU). Putative and reported terminators with the scores above our ch osen threshold were found for 37 of the 53 non-coding RNA TU and for almost 50% of the 2592 annotated protein-encoding TU, which correlates well with the number of TU expected to contain rho-independent terminators. We also i dentified 439 terminators that could function in a bi-directional fashion, servicing one gene on the positive strand and a different gene on the negat ive strand. Approximately 700 additional termination signals in non-coding regions (NCR) far away from the nearest annotated gene were predicted. This number correlates well with the excess number of predicted 'orphan' promot ers in the NCR, and these promoters and terminators may be associated with as yet unidentified TU. The significant number of high scoring hits that oc curred within the reading frame of annotated genes suggests that either an additional component of rho-independent terminators exists or that a suppre ssive mechanism to prevent unwanted termination remains to be discovered.