Function of ribonuclease H in initiation of DNA replication in Escherichia coli K-12.
Escherichia coli rnh mutants lacking ribonuclease H (RNase H) activity can tolerate deletion of the origin of DNA Replication (delta oriC) and transposon-insertional inactivation of an initiator gene (dnaA::Tn10). Introduction of the recA200 allele encoding a thermolabile RecA protein into rnh- dnaA::Tn10 and rnh- delta oriC mutants strains rendered DNA synthesis and colony formation of these mutants temperature sensitive. The temperature sensitivity and the broth sensitivity (Srm-) of the rnh- dnaA::Tn10 recA200 strain was suppressed by the presence of plasmids (pBR322 derivatives) carrying dnaA+ only when the intact oriC site was present on the chromosome. Lack of RNase H activity neither promoted replication of minichromosomes (pOC24 and p lambda asn20) in the absence of required DnaA+ protein nor inhibited dnaA+-dependent minichromosome replication. These results led to the conclusion that RNase H is not directly involved in the events leading to initiation of DNA replication at oriC. Rather, it functions as a specificity factor by eliminating certain forms of RNA-DNA hybrids which could otherwise be used to prime DNA replication at sites other than oriC.
Kogoma
T
T
Subia
N L
NL
von Meyenburg
K
K
D002872:Chromosome Deletion; D004261:DNA Replication; D004262:DNA Restriction Enzymes; D004722:Endoribonucleases / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005838:Genotype; D007700:Kinetics; D009154:Mutation; D010957:Plasmids; D016914:Ribonuclease H; D013045:Species Specificity; D013816:Thermodynamics
D004722:Endoribonucleases; D004262:DNA Restriction Enzymes; D016914:Ribonuclease H