Expression profiles of dnaA null, rok null, and dnaA null; rok null mutants
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ABSTRACT: To identify potential targets of co-regulation by DnaA and Rok, we compared the transcriptional profiles of dnaA null, rok null, and dnaA null rok null mutants. Because a dnaA null mutant requires an oriC- strain background, we used an oriC- oriN+ background for all strains, to allow direct comparisons. We compared biological triplicates for each of the following strains: dnaA null (CAL2074), rok null (CAS196), dnaA null rok null (CAS192), and dnaA+ rok+ (CAL2083; control).
Project description:To identify potential targets of co-regulation by DnaA and Rok, we compared the transcriptional profiles of dnaA null, rok null, and dnaA null rok null mutants. Because a dnaA null mutant requires an oriC- strain background, we used an oriC- oriN+ background for all strains, to allow direct comparisons.
Project description:Assays 1-4: Effects of DnaA activity on S. meliloti chromosome, pSymA and pSymB replicon bias. Sheared DNA extracts of IPTG-induced vs uninduced cultures of DnaA (Assays 1,2) or Hda (Assays 3,4) overexpressors were labeled with Cy3 or Cy5 and hybridized applying dye-swap replicate design. Assay 5: Hybridization of sheared DNA of logarithmic (Cy3-labeled) vs stationary phase (Cy5-labeled) culture.
Project description:Double-strand breaks (DSBs) can lead to the loss of genetic information and cell death. Consequently, cells in all domains of life have evolved mechanisms to repair DSBs, including through homologous recombination. Although recombination has been well characterized, the spatial organization of this process in living cells remains poorly understood. Here, we introduced site-specific DSBs in Caulobacter crescentus, and then used time-lapse microscopy to visualize the homology search, DSB repair, and the resegregation of chromosomal DNA. Even loci tethered to opposite cell poles can efficiently release, pair to enable recombination-based repair, and then resegregate to their original locations. Resegregation occurs independent of DNA replication and without disrupting global chromosome organization. Origin-proximal regions are resegregated by the same machinery, ParABS, used to segregate undamaged chromosomes following DNA replication. In contrast, origin-distal regions efficiently resegregate after a DSB independent of ParABS, and likely without dedicated segregation proteins. Instead, we propose that a physical, spring-like force drives the resegregation of origin-distal loci after DSB repair. Caulobacter cells were depleted of DnaA for 1.5 h before synchronization. Swarmer cells were then released into DnaA depleting conditions (without IPTG) and double-strand breaks were induced for 1 h by the addition of 500 ?M vanillate. For control sample, no vanillate was added. Formadehyde (Sigma) was then added to the final concentration of 1%. Formadehyde crosslinks protein-DNA and DNA-DNA together, thereby capturing the structure of the chromosome at the time of fixation. Fixation was performed at the cell density of OD600 = 0.2. The crosslinking reactions were allowed to proceed for 30 minutes at 25 °C before quenching with 2.5 M glycine at a final concentration of 0.125 M. Fixed cells were then pelleted by centrifugation and subsequently washed twice with 1x M2 buffer (6.1 mM Na2HPO4, 3.9 mM KH2PO4, 9.3 mM NH4Cl, 0.5 mM MgSO4, 10 ?M FeSO4, 0.5 mM CaCl2) before resuspending in 1x TE buffer (10 mM Tris-HCl pH 8.0 and 1 mM EDTA) to a final concentration of 107 cells per µl. Resuspended cells were then divided into 25 µl aliquots and stored at -80 °C for no more than 2 weeks. Each Hi-C experiment was performed using two of the 25 µL aliquots. Chromosome conformation capture with next-generation seqeuncing (Hi-C) was carried out exactly as described previously (Le et al., 2013 PMID: 24158908)
Project description:Initiation of DNA replication requires binding of the initiator protein, DnaA, to specific binding sites in the chromosomal origin of replication, oriC. In low G+C Gram-positive bacteria, the primosomal proteins DnaD and DnaB, in conjunction with loader ATPase DnaI, load the replicative helicase at oriC, and this depends on DnaA. DnaD and DnaB are also required to load the replicative helicase outside of oriC during replication restart, in a DnaA-independent manner. DnaA also binds to many sites around the chromosome, outside of oriC, and acts as a transcription factor at several of these. Using chromatin immunoprecipitation, we found that DnaD and DnaB, but not the replicative helicase, are associated with many of the chromosomal regions bound by DnaA in vivo in Bacillus subtilis. This association was dependent on DnaA and the order of recruitment was the same as that at oriC, but was independent of a functional oriC. The presence of DnaD and DnaB at the secondary (non-oriC) targets of DnaA in the absence of helicase loading indicates a possible role for DnaD and DnaB in modulating the activity of DnaA. The genome-wide binding profiles of DnaA, DnaD, DnaB and DnaC were determined. Binding profiles were determined in exponentially growing cells with and without HPUra treatment. Three biological replicates were analyzed per protein/treatment (one per array). Enrichment in immunoprecipitated samples versus total genomic DNA were determined.
Project description:Myc oncoproteins are essential regulators of the growth and proliferation of mammalian cells. In Drosophila the single ortholog of Myc (dMyc), encoded by the dm gene, influences organismal size and the growth of both mitotic and endoreplicating cells. A null mutation in dm (dm4) results in attenuated endoreplication and growth arrest early in larval development. Gene expression analysis indicates that loss of dMyc leads to decreased expression of genes required for ribosome biogenesis and protein synthesis. Drosophila larvae were collected 24 hours after egg deposition. Sample comparisons were performed using 3 biological independent experimental replicates of dm4 that were each compared to a common reference (wild type larvae of the same genetic background as dm4). For each comparison, a dye-swapped technical replicate was also performed and the paired results were averaged and used as a single observation.
Project description:ChIP-seq was performed to map the association of SPA-tagged DnaA across the Escherichia coli MG1655 chromosome during exponential phase growth in LB. As a control to remove background, ChIP-Seq was also performed on SPA-tagged AcpS, a protein that is not known to bind DNA.
Project description:We investigated the genome-wide DNA binding of the chromosome partitioning and sporulation protein and ParB family member Spo0J in Bacillus subtilis using chromatin immunoprecipitation and DNA microarrays. We identified ten parS loci to which Spo0J binds, two of which were unexpectedly distant (>1 Mb) from the origin of replication. We used all ten sites to refine the consensus sequence for parS. We found that Spo0J spreads along the DNA around each site. Binding was near maximal levels up to 1.6 kb away from parS, and significantly above background as far away as 18 kb. Deletion of soj (parA) had no detectable effect on spreading. In contrast, the spo0J93 allele appeared to cause a significant decrease in spreading in vivo, without significantly affecting the DNA binding affinity in vitro. spo0J93 causes a phenotype similar to that of a spo0J null mutant and alters the region thought to be involved in interaction between Spo0J dimers. Our findings indicate that spreading is important for in vivo function of Spo0J. Gene expression in areas near parS sites was similar in wild-type and a spo0J null mutant, indicating that binding and spreading of Spo0J on DNA does not silence transcription of nearby genes. Keywords: genetic modification Gene expression was compared in spo0J mutant and wild-type B. subtilis by isolating total RNA from three independent cultures of each strain and comparing them on microarrays. One of the arrays (GSM152506) used the reverse dye assignments relative to the other two.