DNA from diverse sources manifests cryptic low‐level transcription in Escherichia coli

Abstract

Summary: We present evidence that DNA from diverse prokaryotic and eukaryotic sources gives rise to low‐level fusion expression in Escherichia coli promoter‐probe vectors. This expression may be as high as 10% of the E coli lac UV5 promoter. Although expression does not correlate with the presence of obvious E. coli promoter‐like sequences, it is blocked by transcriptional terminators. Furthermore, transcription across the fusion junction is detected at levels that correlate with fusion expression. We suggest that this Mow‐level transcription'(LLT) results from infrequent initiation by RNA polymerase at random sites and/or weak promoters. We propose that LLT has biological significance. In some instances, it may provide an advantageous basal level of gene expression, and we suggest that this may be true for the E. coli lac Y gene. In other instances, LLT may be detrimental, in which case it may be blocked by mechanisms such as RNA secondary structure or transcriptional polarity. We present evidence to show that activation of the IS 10 transposase gene by LLT is blocked at the translational level.