The Defects In Ribosome Function Affect Initiation Of Chromosome Replication In Escherichia Coli

To see the effect of defects in ribosome function on initiation of chromosome replication in Escherichia coli, we investigated the roles of ribosomal proteins RpsF、 RpsO、Sra and ribosome-associated proteins YfiA、RimJ、 RMF、DbpA、HPF in initiation of replication. We found that initiation of replication of △sra、△rpsF、 △rpsO、△yfiA、△rimJ、△rmf、△dbpA、△hpf mutant cells was delayed, and cell sizes of these mutants were changed compared with the wild-type cells. The delay in initation of replication and the decrease in cell size of △sra and ArimJ mutant cells were dramatic. Introduction of individual allele of these mutants to dnaB252 or dnaC2 mutant which is inactived at the non-permissive temperature did not change the temperature sensitivity of dnaB252 or dnaC2. The results indicate that RpsF^ RpsO、Sra、YfiA、RimJ、RMF、DbpA and HPF do not have a direct interation with DnaB and DnaC. Interestingly, absence of RpsF、RpsO、Sra、YfiA、RimJ、RMF、 DbpA or HPF protein affects the amount of total protein content and the DnaA protein per cell. Especially, the amount of total protein content and the DnaA protein per cell were significantly decreased in Asra and ArimJ cells.Although overexpression of Sra from pACYC177-sra and psra-gfp could not reverse the phenotype of the △sra mutant, overexpression of Sra increased the-amount of total protein content and the DnaA protein per cell. In addition, plasmid pACYC177-rimJ did not reverse the phenotype of ArimJ mutant. Further analysis showed that pET28a-rimJ did not produce the RimJ protein.As a summary, the defects in ribosome function affect initiation of chromosome replication through changing the synthesis of total protein and subsequent DnaA.