Expression of the DeaD RNA Helicase Is Regulated at Multiple Levels through Its Long mRNA 5' Untranslated Region.

DEAD-box proteins (DBPs) are a prominent class of RNA remodeling proteins that alter RNA structure, a process they typically perform through an ATP-dependent RNA helicase activity. Although many DBPs have been characterized at the structural and functional level in detail, much less is known about how they are regulated. We previously showed that the mRNA for the Escherichia coli DeaD DBP contains an unusually long 5' untranslated region (5' UTR) of 838 nucleotides (nt) and that it is the primary RNA determinant of DeaD autoregulation. We speculated that such a long and complex 5' UTR might regulate deaD expression in additional ways. Here, we show that the deaD mRNA 5' UTR regulates deaD expression at two additional levels, temperature-dependent expression and through a stem-loop structure overlapping the start codon. These results support the hypothesis that a long 5' UTR can regulate gene expression through multiple mechanisms. IMPORTANCE The expression of genes is frequently regulated by determinants in the 5' UTR. Although many different regulatory mechanisms that operate via the 5' UTR have been described, the functional relevance of genes with long UTRs is less clear. Here, we show that the 838-nt-long 5' UTR in the deaD mRNA regulates the expression of DeaD at multiple levels. We propose that long UTRs originate to provide precise control of gene expression through multiple regulatory mechanisms, and they are indicators of the importance of their associated gene products for cellular adaptation to different environments.