Initiation of DNA Replication by Primer Proteins: Bacteriophage ø29 and Its Relatives
The fact that none of the known DNA polymerases is able to initiate DNA chains but only to elongate from a free 3′-OH group raises the problem of how replication is initiated, both at the replication origin and on Okazaki fragments. It was first shown by A. Kornberg et al. that a general mechanism to initiate replication is through the formation of an RNA primer catalyzed by RNA polymerases or by a new class of enzymes, the primases (Kornberg 1980). This mechanism, which can be used in the case of circular DNA molecules or linear DNAs that circularize or form concatemers, cannot be used at the ends of linear DNAs since the RNA primer is removed from the DNA chain, and there is no way of filling the gap resulting at the 5′-ends of the newly synthesized DNA chain. In some cases linear DNA molecules contain a palindromic nucleotide sequence at the 3′-end that allows the formation of a hairpin structure which provides the needed free 3′-OH group for elongation. This mechanism, first proposed by Cavalier-Smith (1974) for eukaryotic DNA replication, was shown to take place in several systems (Kornberg 1980, 1982). Another mechanism to initiate replication consists in the specific nicking of one of the strands of a circular double-stranded DNA, producing a 3′-OH group available for elongation (Kornberg 1980). In the case of the Bacillus subtilis phage ø 29, which contains a linear, double-stranded DNA of molecular weight 11.8 × 106 (Sogo et al. 1979), the initiation of replication cannot take place by any of the indicated mechanisms. In this review I will describe the existence of a protein covalently linked to the ends of ø 29 DNA as well as to the DNA ends of phages related to ø 29 and its role in the initiation of replication by a protein-priming mechanism (Salas 1983).
KeywordsInverted Terminal Repeat Exonuclease Activity Initiation Complex Initiation Reaction Covalent Complex
Unable to display preview. Download preview PDF.
- Carrascosa JL, Camacho A, Moreno F, Jiménez F, Mellado RP, Viíïuela E, Salas M (1976) Bacillus subtilis phage ø 29: characterization of gene products and functions. Eur J Biochem 66: 229–241Google Scholar
- Daubert SD, Bruening G (1984) Detection of genome-linked proteins of plants and animal viruses. Methods Virol 8: 347–379Google Scholar
- Fuèik V, Grunow E, Grünnerovâ H, Hostomskÿ Z, Zadrazyl S (1980) New members of Bacillus subtilis phage group containing a protein link in their circular DNA. Zadrazyl S, Sponar J, (eds) In DNA: recombination, interactions and repair. Pergamon, New York, pp 111–118Google Scholar
- Garcia JA, Pastrana R, Prieto I, Salas M (1983 b) Cloning and expression in Escherichia coli of the gene coding for the protein linked to the ends of Bacillus subtilis phage q5 29 DNA. Gene 21: 65–76Google Scholar
- Geiduschek EP, Ito J (1982) Regulatory mechanisms in the development of lytic bacteriophages in Bacillus subtilis. In: Dubnau DA (ed) The Molecular Biology of the Bacilli. Academic, London, 1: 203–245Google Scholar
- Henney DJ, Hoch JA (1980) The Bacillus subtilis chromosome. Microbiol Rev 44: 57–82Google Scholar
- Kornberg A (1980) DNA replication. Freeman, San FranciscoGoogle Scholar
- Kornberg A (1982) DNA replication supplement. Freeman, San FranciscoGoogle Scholar
- Mellado RP, Pefialva MA, Inciarte MR, Salas M (1980) The protein covalently linked to the 5’ Initiation of DNA Replication by Primer Proteins: Bacteriophage ø 29 and Its Relatives 87 termini of the DNA of Bacillus subtilis phage ø 29 is involved in the initiation of DNA replication. Virology 104: 84–96PubMedCrossRefGoogle Scholar
- Salas M, Prieto I, Gutiérrez J, Blanco L, Zaballos A, Lâzaro JM, Martin G, Bernad A, Garmendia C, Mellado RP, Escarmis C, Hermoso JM (1987) Replication of phage ø 29 DNA primed by the terminal protein. In: Kelly T, McMacken R (eds) Mechanisms of DNA replication and recombination. UCLA symposia on molecular and cellular biology, new series, vol 47. Liss, New York, pp 215–225Google Scholar