ABSTRACT
Changing mRNA stability is a major post-transcriptional way of controlling gene expression, particularly in newly encountered conditions. As the concentration of mRNA is the result of an equilibrium between transcription and degradation, it is generally assumed that at constant transcription, any change in mRNA concentration is the consequence of mRNA stabilization or destabilization. However, the literature reports many cases of opposite variations in mRNA concentration and stability in bacteria. Here, we analyzed the causal link between the concentration and stability of mRNA in two phylogenetically distant bacteria Escherichia coli and Lactococcus lactis. Using reporter mRNAs, we showed that modifying the stability of an mRNA had unpredictable effects, either higher or lower, on its concentration, whereas increasing its concentration systematically reduced stability. This inverse relationship between the concentration and stability of mRNA was generalized to native genes at the genome scale in both bacteria. Higher mRNA turnover in the case of higher concentrations appears to be a simple physical mechanism to regulate gene expression in the bacterial kingdom. The consequences for bacterial adaptation of this control of the stability of an mRNA by its concentration are discussed.
Subject(s)
Escherichia coli/genetics , Gene Expression Regulation, Bacterial , Lactococcus lactis/genetics , RNA Stability , RNA, Messenger/genetics , Base Sequence , Genome, Bacterial/genetics , RNA, Bacterial/genetics , RNA, Bacterial/metabolism , RNA, Messenger/metabolism , Species SpecificityABSTRACT
Amylosucrase is a transglucosidase that catalyses the synthesis of an amylose-type polymer from sucrose, an abundant agro-resource. Here we describe a novel thermostable amylosucrase from the moderate thermophile Deinococcus geothermalis (DGAS). The dgas gene was cloned and expressed in Escherichia coli. The encoded enzyme was purified and characterized. DGAS displays a specific activity of 44 U mg(-1), an optimal temperature of 50 degrees C and a half-life of 26 h at 50 degrees C. Moreover, it produces an alpha-glucan at 50 degrees C, with an average degree of polymerization of 45 and a polymerization yield of 76%. DGAS is thus the most active and thermostable amylosucrase known to date.