Arch. Biol. Med. Exp. 13, 213-232, 1980 The Enzymology of DNA Replication La enzimología de la replicación de DNA RAFAEL VICUNA Laboratorio de Bioquímica. Instituto de Ciencias Biológicas. Universidad Católica de Chile. Casilla 1 14-D. Santiago, Chile. (Recibido el 26 de marzo de 1980) I. INTRODUCTION 213 2. THE INITIATION REACTION 214 2.1. E. dili priming proteins —dna G gene product —RNA polymerase 2.2. Bacteriophage-coded DNA primases —14 DNA primase —T7 gene 4 protein 2.3. Other primases 2.4. Initiation by a site-specific endonucleolytic cut —0X 174 gene A and fd gene II proteins 3. THE ELONGATION REACTION 217 3.1. E. coli DNA polimerases —E. coli DNA polymerase I —E. cob DNA polymerase 111 3.2. Bacteriophage-coded DNA polymerases —T4 gene 43 protein —T7 gene 5 protein 3.3. DNA polymerases a, B and 7 from eukaryo- tic cells 4. SEALING OF DNA FRAGMENTS 219 4.1. E. coli DNA ligase 4.2. Bacteriophage T4 gene 30 protein 4.3. Mammalian DNA ligases I and II CONFORMATIONAL CHANGES OF DNA DURING REPLICATION 220 5.1. E. coli HDP 5.2. Bacteriophage-coded HDPs —T4 gene 32 protein —T7 HDP —fd gene V protein 5.3. Eukaryotic HDPs 5.4. Bacterial DNA topoisomerases —Swivelases —DNA gyrase 5.5. Bacteriophage-coded DNA topoisomerases —T4 DNA topoisomerase —Lambda int gene product —0X174 gene A and fd gene II proteins 5.6. Eukaryotic DNA topoisomerases 5.7. E. coli DNA helicases —DNA helicase I —DNA helicase II —rep protein —rec BC nuclease 5.8. Bacteriophage-coded DNA helicases —T4 gene dda protein —T7 gene 4 protein 5.9. Eukaryotic DNA helicases CONCLUSIONS 227 REFERENCES '227 APPENDIX 232 1. INTRODUCTION Progress made during the last years in our knowledge of DNA replication has shown that it is a somewhat complex process (for recent reviews see refs 1-6). Attempts to elucidate the mechanism of DNA synthesis have been undertaken using simple templates, such as bacterial and animal viral chromosomes and plasmids. All these systems have shown that several proteins are required to initiate and elongate DNA chains, as well as to bring about the topological changes the DNA molecule must undergo during its duplication. The requirement for these proteins can be directly demonstrated with the utilization of thermosensitive mutants, by using specific inhibitors and by reconstitution of an in vitro replication system with the purified components. Although in some cases 'The abbreviations used are: ss: single stranded; ds: double stranded; NEM: N-ethyimaleimide; DNA pol: DNA polymerase; M. W.: molecular weight; ddTTP: 2'3' dideoxythymidine triphosphate; HDP: helix destabilising protein; RF: replicative form; EF: elongation factor; SDS: sodium dodecyl sulfate.