RNA-LINKED NASCENT DNA PIECES IN PHAGE-T7-INFECTED ESCHERICHIA-COLI .3. DETECTION OF INTACT PRIMER RNA

RNA-linked DNA fragments of T7-lnfected Escherlchla coli were labeled with [32P]orthophosphate In vivo. The RNA segments of the labeled fragments were Isolated by degrading the DNA portion with the 3′→ 51 exo-nuclease intrinsic to bacterlophage T4 DNA polymerase and fractionated according to net charge by a DEAE-Sephadex A-25 column chromatography in the presence of 7 M urea. Tri-, tetra- and pentanucleotldes were obtained which have ATP residues at their 5′ ends. Most of the pentanucleotides had a single deoxynucleotlde at the 3′ end but a minor portion was totally an ollgoribonucleotlde. In the light of prior results, the former is a cooligomer of an intact tetraribonucleotide primer and a monodeoxynucleotide and the latter is an intact pentarlbonucleotide primer. Tri- and tetraribonucleotides with ATP at the 5′ ends had no deoxynucleotide at the 3′ ends, therefore it is not clear if intact triribonucleotide primers are present. The 5′-terminal di-nucleotides of the tetra- and pentanucleotides were mostly pppApC and a trace amount of pppApA was present. © 1979 Information Retrieval Limited.