Chip-chip from E. coli MG1655 cells with different methods to detect SeqA and σ32 binding and causes of high background. Escherichia coli str. K-12 substr. MG1655

Reinvestigation of the chromatin immunoprecipitation procedure led us to discover four causes of high background: non-unique sequences, incomplete reversion of crosslinks, washing with spin-columns and insufficient RNase treatment. We used a publishd method giving a high background signal and a modified chromatin immunoprecipitation method which could greatly reduce the false positive rate and apply it to analyze genome wide binding of SeqA and σ32 binding in E. coli. Overall design: RNA polymerase binding in wt E. coli MG1655 with old method (two biological relpicates); comparison of SeqA-binding to wt with old and modified method (two biological replicates each); comparison of SeqA-binding with old and modified method to E. coli ΔseqA (one array each); comparison of crosslinked/reversed to non crosslinked E. coli chrom. DNA; σ32 binding at 30°C and 43°C (two biological replicates each); σ32 binding at 30°C and 43°C with shortened RNase digestion during ChIP (one array each).