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Regulation of the bacteriophage Mu gem operon
G Fabozzi1, L Paolozzi, P Ghelardini
1Centro Studi per gli Acidi Nucleici del CNR, Rome, Italy.
Abstract:
The gem operon of bacteriophage Mu, responsible for the complex phenomenon of phage conversion, is included in the so called "semiessential early" region of phage DNA. Unlike the other early genes of the phage which are transcribed from the pe promoter, expression of the gem operon is driven by its own promoter, which escapes the control of the repressor. In fact, the transcript corresponding to gem was detected in immune lysogens by using a combined reverse transcription and a subsequent amplification of the resulting cDNA. The transcription initiation site from pgem was determined by primer extension mapping experiments and localized at 8217 bp from the left end of phage DNA. Two elements which could perform the negative control of gem were also identified. The first is a phage product, GemB, which presumably interferes with gem expression at a posttranscriptional level, whereas the second is a structural element, an inverted repeat immediately downstream of pgem, which acts as a terminator for the transcripts starting from pe. These transcripts could regulate gem expression by interfering with the initiation of transcription from pgem.
Insights
Bacteriophage Mu's gem operon, crucial for phage conversion, has its own promoter that bypasses repressor control. Researchers identified two negative regulatory elements, GemB and an inverted repeat, affecting gem expression.
Area of Science:
- Molecular biology
- Virology
- Genetics
Background:
- The gem operon in bacteriophage Mu is involved in phage conversion.
- It resides in the "semiessential early" region of phage DNA.
- Unlike other early genes, gem expression is regulated by its own promoter, pgem, independent of repressor control.
Purpose of the Study:
- To investigate the regulation of the bacteriophage Mu gem operon.
- To identify the transcription initiation site of pgem.
- To elucidate the mechanisms of negative control over gem expression.
Main Methods:
- Reverse transcription and cDNA amplification to detect gem transcripts in immune lysogens.
- Primer extension mapping to determine the transcription initiation site of pgem.
- Identification of regulatory elements through genetic and molecular analyses.
Main Results:
- The gem operon's transcript was detected in immune lysogens, confirming its expression.
- The transcription initiation site of pgem was mapped to 8217 bp from the left end of phage DNA.
- Two negative regulatory elements were identified: the phage product GemB (post-transcriptional interference) and an inverted repeat downstream of pgem (transcriptional termination).
Conclusions:
- The gem operon possesses an independent promoter (pgem) that escapes repressor control.
- Gem expression is negatively regulated by both a phage product (GemB) and a structural DNA element acting as a terminator.
- These regulatory mechanisms ensure precise control over gem operon expression during bacteriophage Mu infection.