RNA-linked nascent DNA pieces in phage T7-infected Escherichia coli. III. Detection of intact primer RNA.

RNA-linked DNA fragments of T7-infected Escherichiacoli were labeled with [(32)P]orthophosphate invivo. The RNA segments of the labeled fragments were isolated by degrading the DNA portion with the 3'--> 5' exonuclease intrinsic to bacteriophage 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 pentanucleotides were obtained which have ATP residues at their 5' ends. Most of the pentanucleotides had a single deoxynucleotide at the 3' end but a minor portion was totally an oligoribonucleotide. 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 pentaribonucleotide 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 dinucleotides of the tetra- and pentanucleotides were mostly pppApC and a trace amount of pppApA was present.Images