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Bacteriophage P4 DNA replication. Nucleotide sequence of the P4 replication gene and the cis replication region
1Department of Molecular Biology, University of California, Berkeley 94720.
Abstract:
A 3100 base piece of DNA from the 11,500 base genome of bacteriophage P4 was analyzed for its nucleotide sequence. This segment of DNA contains two open reading frames of 106 and 777 amino acid residues; the latter of which is the coding sequence for the Mr 84,841 alpha protein, which is necessary for P4 DNA replication and is thought to act as a P4-specific DNA primase. A region of about 300 base-pairs localized just beyond the alpha gene and about 4500 bases from the origin of replication (ori), was defined as the locus for P4's cis replication region (crr). This region is required for replication both in vivo and in vitro, and consists of two directly repeated sequences of 120 base-pairs that match one another at 98 positions. These directly repeated sequences are separated by 60 base-pairs, which are not necessary for replication. Each repeat in crr contains three copies of the octamer TGTTCACC that is found six times in ori. Either of the 120 base-pair repeat sequences in crr is sufficient for replication, and the entire crr can function in an inverted orientation. crr is also active at a distance of 1800 bases from the P4 origin of replication.
Insights
The P4 bacteriophage
Area of Science:
- Molecular Biology
- Genetics
- Virology
Background:
- Bacteriophage P4 is a satellite virus with a compact genome.
- Understanding P4's replication mechanism is crucial for viral genetics research.
Purpose of the Study:
- To determine the nucleotide sequence of a 3100 base-pair DNA segment of bacteriophage P4.
- To identify genes and regulatory regions involved in P4 DNA replication.
Main Methods:
- DNA sequencing of a 3100 base-pair fragment of the P4 genome.
- Bioinformatic analysis to identify open reading frames and regulatory sequences.
Main Results:
- Identified two open reading frames, including the gene for the alpha protein (Mr 84,841), essential for P4 DNA replication.
- Characterized the cis-replication region (crr), a 300 base-pair locus containing two 120 base-pair direct repeats, crucial for replication.
- Demonstrated that either repeat sequence is sufficient for replication and that crr functions in inverted orientation and at a distance from the origin of replication.
Conclusions:
- The alpha protein likely functions as a P4-specific DNA primase.
- The crr region, with its repeated sequences, plays a vital role in P4 DNA replication initiation and regulation.
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