Characterization of cis-acting mutations which increase expression of a glnS-lacZ fusion in Escherichia coli.

glnS-lacZ fusions have been used to isolate mutations which enhance expression of the glnS gene. One mutation, acting at the level of transcription changes the -10 region of the promoter from GATCAT to TATCAT and produces a ten-fold increase in mRNA. Four other mutations which enhance expression three-fold to nine-fold fall within the transcribed region, but not within the Shine and Dalgarno sequence nor in the initiator codon. These mutations are shown to enhance translation specifically and different models are considered to explain their mode of action.