Transcription termination within the regulatorynifLA operon ofKlebsiella pneumoniae

Abstract

The effect of premature stop codons in thenifL gene on the expression ofnifA-lacZ operon and protein fusions inKlebsiella pneumoniae was analysed in detail. Our results revealed transcriptional polarity in this operon. By dissecting the operon, intragenic regions containing Rho-dependent transcription terminators have been identified. As shown for other Rhodependent terminators, their cytosine content is much higher than the incidence of guanines. However, other regions of the operon that have this feature did not show termination activity, suggesting that, contrary to previous reports, a correlation between these parameters cannot readily be established. Some of our results also suggested that, in addition to polarity, other mechanisms may prevent expression ofnifA when translation ofnifL is altered. Their importance for efficient regulation of nitrogen fixation genes is discussed.