The 5′ untranslated region of fruA mRNA in Myxococcus xanthus positively regulates the expression of its own gene

Myxococcus xanthus provides an excellent model organism for studying the mechanism of multicellular morphogenesis. The mRNA for FruA, a transcription factor essential for the development of M. xanthus, contains a very long 5′-UTR consisting of 235 nucleotides. Using lacZ as a reporter gene, two fruA-lacZ translational fusions retaining or lacking the fruA 5′-UTR were constructed and separately integrated at phage Mx8 attachment site (attB) in M. xanthus chromosome. Deletion in 5′-UTR between nucleotides from +4 to +220 abolished fruA-lacZ expression during develop- ment, indicating that the 5′-UTR is essential for the induction of fruA. Prediction of the RNA secondary structure of 5′-UTR shows that this region could form an extremely sta- ble three-helix junction structure, which might be a binding site for a regulatory protein or contain a cis-acting element(s) to control fruA expression. Thus, the 5′-UTR of fruA mRNA positively regulates the expression of its own gene.