| Summary: | 碩士 === 國立清華大學 === 生物資訊與結構生物研究所 === 92 === Analyses of primosome assembly at chromosomal and plasmid origins as well as that at single-stranded replication origins revealed the presence of two distinct primosomes in Escherichia coli for primer RNA synthesis and duplex unwinding. A DnaA-dependent primosome is assembled at oriC, the chromosomal origin of Escherichia coli, as well as at the A site. In contrast, PriA protein recognizes a hairpin, called PAS (primosome assembly site), and initiates assembly of the ΦX174-type PriA-dependent primosome in conjunction with other prepriming proteins.
Seven primosomal protein, PriA, PriB, PriC, DnaB, DnaC, DnaG and DnaT, are required for the assembly of a primosome at the primosome assembly site (PAS) on a single-stranded DNA-binding protein (SSB)-coatedΦX174 phage DNA. PriB stabilizes PriA on the DNA, this cannot be the sole reason it facilitates binding of DnaT, and it is likely that PriB-induced conformational rearrangements contribute as well. The data presented thus far suggest that PriB acts to facilitate entry of DnaT into a complex with PriA.
We solved the crystal structure of the PriB and dA5mer complex from Escherichia coli at a resolution of 2.8 Å. The crystal of PriB-dA5mer belong to the Monoclinic space group P21 and cell parameter is a=47.4 Å，b=45.67 Å，c= 51.48 Å，β=96.1°。There are two PriB molecules per one asymmetric unit. We solved the phase problem by using MR method from PriB model. The structure of PriB is similar to that of single-stranded DNA binging protein (SSB), even though they share only 16% amino acid sequence identity. We describe here the structure of the PriB complex with dA5mer.
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