Fate of the sblA transcript in Streptomyces lividans and Escherichia coli.

In Streptomyces lividans, the tight temporal regulation of the transient expression of the sblA gene was shown to involve an operator-like sequence located on the sblA transcript. This operator-like structure constitutes a stem-loop structure containing a Shine/Dalgarno-like sequence. Its destruction, by site directed mutagenesis, led to an enhancement of sblA expression. This structure thus plays a negative role in the regulation of sblA expression and might be involved in the regulation of the specific degradation of the sblA transcript. In this issue, the fates of the sblA transcript, in S. lividans and in Escherichia coli, were compared. Analysis of the decay of the sblA transcript revealed that, in both species, the sblA transcript was cleaved just behind the stem-loop structure by an RNAse E-like activity. In E. coli, three discrete products resulting from the cleavage of the full-length transcript by the RNAase E at another site, located 282 nucleotides downstream of the stem-loop structure, were detected whereas only one processed product, corresponding to the 5' end of the gene, was detected in S. lividans. These differences in the mode of degradation of the sblA transcript in S. lividans and E. coli are discussed.