The EMBO Journal Vol.16 No.18 pp.5784–5795, 1997 Plasmid rolling circle replication: identification of the RNA polymerase-directed primer RNA and requirement for DNA polymerase I for lagging strand synthesis M.Gabriela Kramer, Saleem A.Khan1 and (del Solar et al., 1987a; Gruss et al., 1987). It has been Manuel Espinosa2 postulated that lagging strand synthesis is initiated by a primer RNA (pRNA) which is synthesized from the sso Centro de Investigaciones Biolo´gicas, CSIC, Velazquez, 144, (Birch and Khan, 1992; Dempsey et al., 1995). Primer 1 E-28006 Madrid, Spain and Department of Molecular Genetics and synthesis is thought to be performed by the host RNA Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA polymerase (RNAP) since the presence of the RNAP inhibitor rifampicin leads to: (i) in vivo accumulation of 2Corresponding author e-mail:
[email protected] ssDNA (Boe et al., 1989; Kramer et al., 1995); (ii) inhibition of in vitro DNA replication of the RCR plasmid Plasmid rolling circle replication involves generation pLS1 (del Solar et al., 1987b); and (iii) inhibition of in of single-stranded DNA (ssDNA) intermediates. ssDNA vitro DNA synthesis from ssDNA templates prepared from released after leading strand synthesis is converted to various RCR plasmids (Birch and Khan, 1992; Dempsey a double-stranded form using solely host proteins. et al., 1995). However, based on either sequence homo- Most plasmids that replicate by the rolling circle mode logies or partial inhibition by rifampicin, it has been contain palindromic sequences that act as the single proposed that lagging strand replication may also be strand origin, sso.