The DeaD Protein Affects Initiation Of DNA Replication In Escherichia Coli

Escherichia coli contains at least five ATP-dependent DEAD-box RNA helicases including DbpA, SrmB, Rh1B, Rh1E and DeaD. These proteins appear to play important roles in translation and mRNA degradation.The DeaD protein possess an enzyme activity domain at the C-terminal end, playing multi-functions as a cold shock protein. However, it is not clear that whether DeaD affects initiation of DNA replication.The paper found that absence of DeaD led to an earlier initiation of replication in larger cells with slower growth relative to that in wild-type cells at 25℃.The effects was not found at 37℃ and 30C in the absence of DeaD, confirming that DeaD is a cold-shock protein. Overexpression of RNase H from a plasmid did not reverse the early initiation of replication in △deaD to the wild-type replication pattern. Similarly, expression of DeaD did not reverse the △rnh replication pattern. Interestingly, overexpression of RNase R restored the wild-type replication pattern from the △deaD phenotype, and overexpression of DeaD reversed the Arnr phenotype. The results indicate that DeaD and RNase R are functionally complementary. Further analysis showed that the C-terminal D156A and E157A mutations led to loss of DeaD function while D159A mutation did not, indicating that D156A and E157A are essential amino acids for the DeaD activity.As a summary, DeaD is a cold shock protein, affecting initiation of replication at low temperature; RNase R and DeaD are complementary functionally; DeaD degrades RNA in vitro, depending on the C-terminal D156 and E157 residues.