Roles of polyadenylation and nucleolytic cleavage in the filamentous phage mRNA processing and decay pathways in...

Area of Science:

• Bacteriology
• Molecular Biology
• Virology

Background:

• Bacterial messenger RNA (mRNA) processing and decay are crucial for gene expression regulation.
• Filamentous phage f1 mRNAs possess typical bacterial mRNA structures, including a 3' hairpin terminator and susceptibility to RNase E processing.
• Polyadenylation's role in bacterial mRNA decay is not fully understood.

Purpose of the Study:

• To elucidate the basic features of mRNA processing and decay pathways in Escherichia coli.
• To investigate the role of polyadenylation in the degradation of f1 phage mRNAs.
• To understand how mRNA decay mechanisms contribute to persistent phage infection.

Main Methods:

• Analysis of f1 phage mRNAs in wild-type and poly(A) polymerase-deficient Escherichia coli hosts.
• Identification and characterization of processed mRNA fragments and small RNAs using molecular techniques.
• Investigation of RNase E cleavage sites and the influence of ribosome binding on processing.

Main Results:

• A subset of f1 mRNAs were found to have poly(A) tails attached at variable positions near the 3' end.
• In poly(A) polymerase-deficient hosts, processed mRNAs were stabilized, and a novel ~125-nucleotide RNA fragment accumulated.
• This 125-nt RNA originates from the 3'-terminal region via RNase E cleavage, normally protected by translating ribosomes.
• Polyadenylation contributes to the degradation of processed mRNAs and is essential for the turnover of the 125-nt fragment, acting as a later-step factor in decay.

Conclusions:

• Bacterial mRNA decay primarily involves endonucleolytic cleavage, with polyadenylation playing a role in later degradation stages, not initiation.
• Stably structured 3' RNA ends, like hairpin terminators, effectively block 3' to 5' exonucleolytic decay.
• These findings clarify f1 mRNA processing and decay pathways, explaining their role in persistent phage infection.