Mutations in a new chromosomal gene of Escherichia coli K-12, pcnB, reduce plasmid copy number of pBR322 and its derivatives
A ribonuclease which degrades RNA specifically in RNA. DNA hybrid structures has been purified X00-fold from Escherichia co2i B and ZOO-fold from E. coli strain DllO pot A1, endo I-, fhy-). For maximal activity, the enzyme requires MgZ+ and the presence of a sulfhydryl reagent. The enzyme is capable of digesting more than 95% of the RNA in RNA .DNA hybrids to acid-soluble products. The products are oligonucleotides with S-phosphate and 3’hydroxyl termini. The enzyme acts as an endonuclease and does not require free 3’ or 5’ termini for activity. However, it cannot cleave the phosphodiester bond covalently linking ribonucleotides to DNA. With circular single stranded DNA templates deoxynucleotide incorporation catalyzed by DNA polymerase II is dependent on RNA synthesis. This reaction can be stimulated by RNase H. During these studies an additional ribonuclease H activity was detected in E. coli B and purified 160-fold. Unlike RNase H, this activity is N-ethylmaleimide-resistant and sensitive to antiserum prepared against DNA polymerase I and attacks [3’-3H,5’-32P]po1y(A) .poly(dT) in the 5’ + 3’ direction.