Question: why origins of replication in dna are usually at-rich

title: Origin of replication
text: The genome of E. coli consists of a single circular DNA molecule of approximately 4.6 x 10 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 . 

Answer: answer: The genome of E. coli consists of a single circular DNA molecule of approximately 4.6 x 10 nucleotide pairs . In E. coli , the origin of replication -- oriC -- consists of three A -- T rich 13 - mer repeats and four 9 - mer repeats .
answer: The origin of replication, oriC, consists of three AT 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 .