DnaA

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Chromosomal replication initiator protein dnaA
Identifiers
Organism Escherichia coli
(str. K-12 substr. MG1655)
Symbol DnaA
Entrez 948217
RefSeq (Prot) NP_418157.1
UniProt P03004
Other data
Chromosome genome: 3.88 - 3.88 Mb
Bac_DnaA_C
PDB 1j1v EBI.jpg
crystal structure of dnaa domainiv complexed with dnaabox dna
Identifiers
Symbol Bac_DnaA_C
Pfam PF08299
Pfam clan CL0123
InterPro IPR013159
SCOP 1j1v
SUPERFAMILY 1j1v
Bac_DnaA
PDB 2hcb EBI.jpg
structure of amppcp-bound dnaa from aquifex aeolicus
Identifiers
Symbol Bac_DnaA
Pfam PF00308
Pfam clan CL0023
InterPro IPR013317
PROSITE PDOC00771
SCOP 1j1v
SUPERFAMILY 1j1v

DnaA is a protein that activates initiation of DNA replication in prokaryotes.[1] It is a replication initiation factor which promotes the unwinding of DNA at oriC.[1] The onset of the initiation phase of DNA replication is determined by the concentration of DnaA.[1] DnaA accumulates during growth and then triggers the initiation of replication.[1] Replication begins with active DnaA binding to 9-mer (9-bp) repeats upstream of oriC.[1] Binding of DnaA leads to strand separation at the 13-mer repeats.[1] This binding causes the DNA to loop in preparation for melting open by the helicase DnaB.[1]

Function[edit]

The active form DnaA is bound to ATP.[1] Immediately after a cell has divided, the level of active DnaA within the cell is low.[1] Although the active form of DnaA requires ATP, the formation of the oriC/DnaA complex and subsequent DNA unwinding does not require ATP hydrolysis.[2]

The oriC site in E. coli has three AT rich 13 base pair regions (DUEs) followed by four 9 bp regions with the sequence TTAT(C or A)CA(C or A)A.[3] Around 10 DnaA molecules bind to the 9 bp regions, which wrap around the proteins causing the DNA at the AT-rich region to unwind. There are 8 DnaA binding sites within oriC, to which DnaA binds with differential affinity. When DNA replication is about to commence, DnaA occupies all of the high and low affinity binding sites. The denatured AT-rich region allows for the recruitment of DnaB (helicase), which complexes with DnaC (helicase loader). DnaC helps the helicase to bind to and to properly accommodate the ssDNA at the 13 bp region; this is accomplished by ATP hydrolysis, after which DnaC is released. Single-strand binding proteins (SSBs) stabilize the single DNA strands in order to maintain the replication bubble. DnaB is a 5'→3' helicase, so it travels on the lagging strand. It associates with DnaG (a primase) to form the only primer for the leading strand and to add RNA primers on the lagging strand. The interaction between DnaG and DnaB is necessary to control the longitude of Okazaki fragments on the lagging strand. DNA polymerase III is then able to start DNA replication.

DnaA contains two conserved regions: the first is located in the central part of the protein and corresponds to the ATP-binding domain, the second is located in the C-terminal half and is involved in DNA-binding.[4]

References[edit]

  1. ^ a b c d e f g h i Foster JB, Slonczewski J (2009). Microbiology: an evolving science. New York: W.W. Norton & Co. ISBN 0-393-97857-5. 
  2. ^ Leonard AC, Grimwade JE (December 2010). "Regulating DnaA complex assembly: it is time to fill the gaps". Curr. Opin. Microbiol. 13 (6): 766–72. doi:10.1016/j.mib.2010.10.001. PMC 3005629. PMID 21035377. 
  3. ^ Fuller RS, Funnell BE, Kornberg A (October 1984). "The dnaA protein complex with the E. coli chromosomal replication origin (oriC) and other DNA sites". Cell 38 (3): 889–900. doi:10.1016/0092-8674(84)90284-8. PMID 6091903. 
  4. ^ Roth A, Messer W (May 1995). "The DNA binding domain of the initiator protein DnaA". EMBO J. 14 (9): 2106–11. PMC 398312. PMID 7744016. 

Further reading[edit]

  • Pratt CA, Voet D, Voet JG (2012). Fundamentals of Biochemistry: Life at the Molecular Level. New York: Wiley. ISBN 0-470-54784-7. 
  • Cox M, Nelson DR (2008). Lehninger Principles of Biochemistry. W H Freeman & Co (Sd). ISBN 1-4292-2416-9. 

External links[edit]

This article incorporates text from the public domain Pfam and InterPro IPR013159

This article incorporates text from the public domain Pfam and InterPro IPR013317