Skip to main content
PMC home page
Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1986 Dec;83(24):9645–9649. doi: 10.1073/pnas.83.24.9645

Positive and negative roles of an initiator protein at an origin of replication.

M Filutowicz, M J McEachern, D R Helinski
PMCID: PMC387197  PMID: 3540947

Abstract

The properties of mutants in the pir gene of plasmid R6K have suggested that the pi protein plays a dual role; it is required for replication to occur and also plays a role in the negative control of the plasmid copy number. In our present study, we have found that the pi level in cell extracts of Escherichia coli strains containing R6K derivatives is surprisingly high (approximately equal to 10(4) dimers per cell) and that this level is not altered in cells carrying high copy number pir mutants. The wild-type and a high copy mutant (Cos405) pir gene were inserted downstream of promoters of different strengths to measure the copy number of an R6K gamma replicon as a function of a 1000-fold range of intracellular pi concentrations. The data demonstrate that reducing the intracellular level of pi to 5% of its normal value can result in a substantial increase in copy number of a gamma origin replicon and that a pi level less than 1% of normal is still permissive for replication. Conversely, increasing the pi level even a few-fold above normal results in a marked inhibition of replication of plasmids containing a single, two, or all three of the R6K origins (alpha, beta, and gamma). We have also shown that the replication inhibition mediated by excess pi is greatly reduced by the pir405 Cos mutation. These results demonstrate that the total level of pi protein is not rate-limiting for a gamma replicon. We have also determined the sensitivity of the pir gene promoter to a wide range of pi concentrations. The activity of this promoter is stimulated by very low pi levels and is almost entirely inhibited when the protein is overproduced 2-fold.

Full text

PDF

Images in this article

9646Image
on p.9646
9646Image
on p.9646
9646Image
on p.9646
9647Image
on p.9647
9648Image
on p.9648
9648Image
on p.9648

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Crosa J. H., Luttropp L. K., Falkow S. Use of autonomously replicating mini-R6K plasmids in the analysis of the replication regions of the R plasmid R6K. Cold Spring Harb Symp Quant Biol. 1979;43(Pt 1):111–120. doi: 10.1101/sqb.1979.043.01.017. [DOI] [PubMed] [Google Scholar]
  2. Crosa J. H. Three origins of replication are active in vivo in the R plasmid RSF1040. J Biol Chem. 1980 Dec 10;255(23):11075–11077. [PubMed] [Google Scholar]
  3. Filutowicz M., Davis G., Greener A., Helinski D. R. Autorepressor properties of the pi-initiation protein encoded by plasmid R6K. Nucleic Acids Res. 1985 Jan 11;13(1):103–114. doi: 10.1093/nar/13.1.103. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Filutowicz M., Uhlenhopp E., Helinski D. R. Binding of purified wild-type and mutant pi initiation proteins to a replication origin region of plasmid R6K. J Mol Biol. 1986 Jan 20;187(2):225–239. doi: 10.1016/0022-2836(86)90230-5. [DOI] [PubMed] [Google Scholar]
  5. Germino J., Bastia D. Interaction of the plasmid R6K-encoded replication initiator protein with its binding sites on DNA. Cell. 1983 Aug;34(1):125–134. doi: 10.1016/0092-8674(83)90142-3. [DOI] [PubMed] [Google Scholar]
  6. Germino J., Bastia D. Rapid purification of a cloned gene product by genetic fusion and site-specific proteolysis. Proc Natl Acad Sci U S A. 1984 Aug;81(15):4692–4696. doi: 10.1073/pnas.81.15.4692. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Germino J., Gray J. G., Charbonneau H., Vanaman T., Bastia D. Use of gene fusions and protein-protein interaction in the isolation of a biologically active regulatory protein: the replication initiator protein of plasmid R6K. Proc Natl Acad Sci U S A. 1983 Nov;80(22):6848–6852. doi: 10.1073/pnas.80.22.6848. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Inuzuka M., Helinski D. R. Replication of antibiotic resistance plasmid R6K DNA in vitro. Biochemistry. 1978 Jun 27;17(13):2567–2573. doi: 10.1021/bi00606a017. [DOI] [PubMed] [Google Scholar]
  9. Inuzuka M., Helinski D. R. Requirement of a plasmid-encoded protein for replication in vitro of plasmid R6K. Proc Natl Acad Sci U S A. 1978 Nov;75(11):5381–5385. doi: 10.1073/pnas.75.11.5381. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Inuzuka N., Inuzuka M., Helinski D. R. Activity in vitro of three replication origins of the antibiotic resistance plasmid RSF1040. J Biol Chem. 1980 Dec 10;255(23):11071–11074. [PubMed] [Google Scholar]
  11. Kelley W., Bastia D. Replication initiator protein of plasmid R6K autoregulates its own synthesis at the transcriptional step. Proc Natl Acad Sci U S A. 1985 May;82(9):2574–2578. doi: 10.1073/pnas.82.9.2574. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Kolter R., Helinski D. R. Construction of plasmid R6K derivatives in vitro: characterization of the R6K replication region. Plasmid. 1978 Sep;1(4):571–580. doi: 10.1016/0147-619x(78)90014-8. [DOI] [PubMed] [Google Scholar]
  13. Kolter R., Helinski D. R. Plasmid R6K DNA replication. II. Direct nucleotide sequence repeats are required for an active gamma-origin. J Mol Biol. 1982 Oct 15;161(1):45–56. doi: 10.1016/0022-2836(82)90277-7. [DOI] [PubMed] [Google Scholar]
  14. Kolter R., Inuzuka M., Figurski D., Thomas C., Stalker D., Helinski D. R. Plasmid DNA replication: RK2- and R6K-encoded trans-acting factors and their sites of action. Cold Spring Harb Symp Quant Biol. 1979;43(Pt 1):91–97. doi: 10.1101/sqb.1979.043.01.014. [DOI] [PubMed] [Google Scholar]
  15. Kolter R., Inuzuka M., Helinski D. R. Trans-complementation-dependent replication of a low molecular weight origin fragment from plasmid R6K. Cell. 1978 Dec;15(4):1199–1208. doi: 10.1016/0092-8674(78)90046-6. [DOI] [PubMed] [Google Scholar]
  16. Kontomichalou P., Mitani M., Clowes R. C. Circular R-factor molecules controlling penicillinase synthesis, replicating in Escherichia coli under either relaxed or stringent control. J Bacteriol. 1970 Oct;104(1):34–44. doi: 10.1128/jb.104.1.34-44.1970. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Laemmli U. K. Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature. 1970 Aug 15;227(5259):680–685. doi: 10.1038/227680a0. [DOI] [PubMed] [Google Scholar]
  18. McEachern M. J., Filutowicz M., Helinski D. R. Mutations in direct repeat sequences and in a conserved sequence adjacent to the repeats result in a defective replication origin in plasmid R6K. Proc Natl Acad Sci U S A. 1985 Mar;82(5):1480–1484. doi: 10.1073/pnas.82.5.1480. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Mukhopadhyay P., Filutowicz M., Helinski D. R. Replication from one of the three origins of the plasmid R6K requires coupled expression of two plasmid-encoded proteins. J Biol Chem. 1986 Jul 15;261(20):9534–9539. [PubMed] [Google Scholar]
  20. Shafferman A., Helinski D. R. Structural properties of the beta origin of replication of plasmid R6K. J Biol Chem. 1983 Apr 10;258(7):4083–4090. [PubMed] [Google Scholar]
  21. Shafferman A., Kolter R., Stalker D., Helinski D. R. Plasmid R6K DNA replication. III. Regulatory properties of the pi initiation protein. J Mol Biol. 1982 Oct 15;161(1):57–76. doi: 10.1016/0022-2836(82)90278-9. [DOI] [PubMed] [Google Scholar]
  22. Southern E. M. Detection of specific sequences among DNA fragments separated by gel electrophoresis. J Mol Biol. 1975 Nov 5;98(3):503–517. doi: 10.1016/s0022-2836(75)80083-0. [DOI] [PubMed] [Google Scholar]
  23. Stalker D. M., Filutowicz M., Helinski D. R. Release of initiation control by a mutational alteration in the R6K pi protein required for plasmid DNA replication. Proc Natl Acad Sci U S A. 1983 Sep;80(18):5500–5504. doi: 10.1073/pnas.80.18.5500. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Stalker D. M., Kolter R., Helinski D. R. Plasmid R6K DNA replication. I. Complete nucleotide sequence of an autonomously replicating segment. J Mol Biol. 1982 Oct 15;161(1):33–43. doi: 10.1016/0022-2836(82)90276-5. [DOI] [PubMed] [Google Scholar]
  25. Towbin H., Staehelin T., Gordon J. Electrophoretic transfer of proteins from polyacrylamide gels to nitrocellulose sheets: procedure and some applications. Proc Natl Acad Sci U S A. 1979 Sep;76(9):4350–4354. doi: 10.1073/pnas.76.9.4350. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Trawick J. D., Kline B. C. A two-stage molecular model for control of mini-F replication. Plasmid. 1985 Jan;13(1):59–69. doi: 10.1016/0147-619x(85)90056-3. [DOI] [PubMed] [Google Scholar]

Articles from Proceedings of the National Academy of Sciences of the United States of America are provided here courtesy of National Academy of Sciences

RESOURCES