The bacteriophage λ cIII gene product is an early regulatory protein that participates in the lysis-lysogeny decision of the phage following infection. We have previously shown that the translation of the cIII gene is determined by two unique factors: (1) efficient expression is dependent upon the presence of RNaseIII in the cell; (2) alternative mRNA structures of the cIII coding region determine the rate of its translation initiation. In this study we demonstrate the presence of the alternative mRNA structures in vivo. The presence of minor RNaseIII cleavage sites within this region indicate that RNaseIII can differentiate between the two alternative structures. We localize by a deletion analysis the RNaseIII responsive element to the cIII coding region, and suggest that regulation of cIII translation by RNaseIII is achieved through binding to the alternative structures region of the mRNA.
Bibliographical noteFunding Information:
We thank Don Court for providing us with purified RNaseIII and me-strains, and for critical reading of this manuscript. We thank R. Traut for supplying us with purified 30 S ribosomal subunits, Ariella Oppenheim for critical reading of this manuscript, and Hilla Giladi for stimulating discussions. This research was supported by a Levi Eshkol grant from the Kational Council for Research and Development, Isreal, to S.A., by grant ROl GM38694-OlAl from the National Institutes of Health, and by the Gesellschaft fiir Biotechnologische Forschung, mbH, Braunschweig. This research was performed, in part, in The Irene and Davide Sala Laboratory for Molecular Genetics.