Hvorfor oprindelsen af replikation i dna normalt er rig?
Origin of replication
E. coli's genom består af et enkelt cirkulært DNA-molekyle på ca. 4,6 x 106 nukleotidpar. DNA-replikation begynder typisk ved et enkelt replikationssted. I E. coli består replikationsoprindelsen-oriC - af tre A-T-rige 13-mer-repeats og fire 9-mer-repeats. Ti til 20 monomerer af replikationsinitiatorproteinet DnaA binder sig til 9-mer-repeterne, og DNA'et vikler sig rundt om dette proteinkompleks og danner en proteinkerne. Denne oprulning stimulerer den AT-rige region i 13-mer-sekvensen til at afvikle sig, så helicase-loader DnaC kan indlæse den replikative helicase DnaB på hver af de to afviklede DNA-strenge. Helicasen DnaB danner grundlaget for primosomet, et enzymkompleks, som DNA-polymerase III rekrutteres til, før replikationen kan finde sted.
Origin of replication
The genome of E. coli consists of a single circular DNA molecule of approximately 4.6 x 106 nucleotide pairs. DNA replication typically begins at a single origin of replication. In E. coli, the origin of replication—oriC—consists of three A–T rich 13-mer repeats and four 9-mer repeats. Ten to 20 monomers of the replication initiator protein DnaA bind to the 9-mer repeats, and the DNA coils around this protein complex forming a protein core. This coiling stimulates the AT rich region in the 13-mer sequence to unwind, allowing the helicase loader DnaC to load the replicative helicase DnaB to each of the two unwound DNA strands. The helicase DnaB forms the basis of the primosome, a complex of enzymes to which DNA polymerase III is recruited before replication can occur .
Origin of replication