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Table 1 Enzymes involved in mRNA degradation and modification during T4 infection.

From: Post-transcriptional control by bacteriophage T4: mRNA decay and inhibition of translation initiation

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