Access Type

Open Access Dissertation

Date of Award


Degree Type


Degree Name



Biological Sciences

First Advisor

Dr. Allen W. Nicholson


Ribonuclease III (RNase III) is a double-stranded-RNA-specific nuclease of Escherichia coli. RNase III functions as a homodimer. The 25.6 kDa subunit contains two domains, a 148 residue catalytic domain and a 78 residue double-stranded-RNA-binding domain (dsRBD). RNase III is involved in the maturation of the 16S and 23S rRNAs, the degradation of mRNA, and the maturation of T7 phage polycistronic early, middle, and late mRNAs. Bacteriophage T7 expresses a protein kinase (T7 PK), which is cAMP-independent, serine/threonine-specific, and phosphorylates over 90 cellular proteins, including RNase III during infection. RNase III processing activity is stimulated from two to eleven-fold upon phosphorylation by the T7 PK. The increase in processing activity is dependent on substrate sequence, and may be important for the efficient maturation of T7 early mRNAs, which are produced in large amounts and contain several RNase III cleavage sites. The increase in activity reflects an increase in the turnover rate of RNase III. The phosphoamino acid has been determined to be serine. The dsRBD as well as the catalytic domain of RNase III is phosphorylated by the T7 protein kinase in vitro.