Transcription signals for stable RNA genes in Methanococcus

Area of Science:

• Archaea microbiology
• Molecular biology
• Gene regulation

Background:

• Previous surveys identified conserved DNA sequences (Box A and Box B) upstream and downstream of tRNA genes in Methanococcus vannielii.
• The functional significance of these conserved sequences in transcription initiation was previously unknown.

Purpose of the Study:

• To investigate the role of conserved Box A and Box B sequences in the initiation of transcription for tRNA and ribosomal RNA genes in Methanococcus.
• To identify transcription termination signals for ribosomal RNA operons in Methanococcus.
• To characterize processing sites for preribosomal RNA maturation.

Main Methods:

• Nuclease S1 mapping experiments were performed on tRNA transcriptional units and a ribosomal RNA operon.
• Utilized protein synthesis inhibition in Methanococcus to accumulate primary transcripts and processing intermediates.
• Analyzed sequence homology and spacing of conserved motifs.

Main Results:

• Transcription initiation consistently occurred at the 'G' within the conserved 'TGC' trinucleotide of Box B, identifying it as a transcription start signal.
• Box A, present in stable RNA transcriptional units but not protein-coding genes, functions as a specific element for stable RNA gene expression.
• Ribosomal RNA operon transcription terminated at an oligo-T stretch downstream of the 5S RNA gene, a signal conserved in stable RNA genes.
• A specific recognition site for a preribosomal RNA processing enzyme was identified.

Conclusions:

• Box B serves as a common transcription start signal in methanogenic and halophilic archaea.
• Box A is essential for the expression of stable RNA genes in Methanococcus.
• Transcription termination signals for stable RNA genes in Methanococcus resemble those in eukaryotes.
• Nuclease S1 mapping effectively identified key regulatory and processing sites in archaeal transcription.