- Escherichia coli DEAD-box protein A (DbpA) is an ATP-dependent RNA helicase with specificity for 23S ribosomal RNA. Although DbpA has been extensively characterized biochemically, its biological function remains unknown. Previous work has shown that a DbpA deletion strain is viable with little or no effect on growth rate. In attempt to elucidate a phenotype for DbpA, point mutations were made at eleven conserved residues in the ATPase active site, which have exhibited dominant-negative phenotypes in other DExD/H proteins. Biochemical analysis of these DbpA mutants shows the expected decrease in RNA-dependent ATPase activity and helix unwinding activity. Only the least biochemically active mutation, R331A, produces small colony phenotype and a reduced growth rate. This dominant slow growth mutant will be valuable to determine the cellular function of DbpA.