Introduction
Posttranscriptional control by mRNA decay
Endoribonuclease RegB and its role in inactivating phage early mRNAs
Functional inactivation of mRNA by RegB
RegB accelerates early mRNA breakdown
The RegB/S1 target site
RegB catalysis and structure
How does S1 activate the RegB cleavage reaction?
Regulation and distribution of the regB gene
What is the role of RegB in T4 development?
T4 Dmd and E. coli RNase LS antagonism
T4 Dmd controls the stability of middle and late mRNAs
Biochemical characterization of RNase LS
The specificity of RNase LS and coupling with translation
The role of RNase LS in E. coli
Other activities implicated in RNA decay during T4 infection
Enzyme | Origin | Reaction catalyzed. Main properties | Role in T4 development |
---|---|---|---|
RNase E |
E. coli
| Endonuclease. Produces 5'-P termini. Activated by 5'-monophosphorylated RNA. Scaffold of the degradosome | Major role in mRNA degradation throughout the phage developmental cycle. |
RNase G |
E. coli
| Endonuclease. Produces 5'-P termini. Activated by 5'- monophosphorylated RNA. | Cuts in the 5' regions of some early RegB processed transcripts. |
RegB | T4 | Sequence-specific endonuclease. Produces 5'-OH termini. Requires S1 r-protein as co-factor | Inactivates early transcripts by cleaving in Shine-Dalgarno sequences. Expedites early mRNA degradation. |
RNase LS |
E. coli
| Endonuclease. Its activity depends on rnlA and rnlB loci. Associated in a multiprotein compex. | Cleaves within T4 middle and late transcripts and expedites their degradation. |
RNase II RNase R Polynucleotide phosphorylase |
E. coli
| 3'-5' exonucleases. PNPase requires 3'-OH termini; the other two are indifferent to the nature of the 3' terminus. | Degrade mRNAs. The relative contribution of each RNase has not been determined. |
PrrC |
E. coli
| tRNAlys anticodon nuclease. Normally silent in E. coli but activated by the T4-encoded Stp polypeptide. | Deleterious to T4 propagation if Pnk or Rli1 enzymes are inactivated. |
Polynucleotide kinase (PNK) | T4 | Phosphorylation of 5'-OH polynucleotide termini. Hydrolysis of 3'-terminal phosphomonoesters and of 2',3'-cyclic phosphodiesters | Counteracts, together with T4 RNA ligase 1, host tRNA anticodon nuclease PrrC. Makes RegB-processed RNA substrates for RNases E and G. |
Dmd | T4 | An early product that binds the RnlA protein, a member of RNase LS | Antagonist of RNase LS |
Poly(A) polymerase |
E. coli
| Addition of poly(A) tails to the 3' end of RNAs | Probably inactivated after T4 infection |
RNA pyrophospho-hydrolase (RppH) |
E. coli
| Hydrolysis of a pyrophosphate moiety from the 5'-triphosphorylated primary transcripts. | Not yet investigated |