Evidence that discontinuous DNA replication in Escherichia coli is primed by approximately 10 to 12 residues of RNA starting with a purine.

Intact primer RNA for discontinuous DNA replication of Escherichia coli has been detected by specific labeling in vitro of its 5'-terminal tri- (or di-) phosphate group with vaccinia guanylyltransferase and [alpha-32P]GTP. A mutant defective either in RNase H or in both RNase H and DNA polymerase I accumulated about 10 or 30 times more intact primer RNA, respectively, than wild-type cells. The primers started with purine in an A to G ratio of 5 and the most abundant 5'-terminal dinucleotide sequence was (p)ppA-Pu. The chain length of the intact primer RNA was approximately 10 to 12 nucleotide residues. The structural properties of the E. coli primer RNa resemble those of the eukaryotic primer RNA.