Fig. 4

HicB stability and RNase assay. Viable cell counts of cells of E. coli strain MG1655 containing pBBara and pNDM220, pBB-hicA and pNDM-hicB or pBB-hicA and pNDM220 that were grown in M63 medium containing or not 0.5 M NaCl (a). Strains were induced with 1 mM arabinose and 1 mM IPTG. Viable cell counts (ten fold dilutions) were determined throughout time, the figure illustrates results obtained 3 h after induction. Cells of E. coli strain BL21 containing pETHicAStrep-HicBHis grown in M63 medium were induced with 1 mM IPTG for 3 h. Half of the culture was centrifuged and protein content was loaded on Strep Tactin and eluted with 1 mM desthiobiotin (b). The other half of the culture was added with 0.5 M NaCl and incubation was extended for 4 h, then the protein content was loaded on Strep-Tactin and eluted with desthiobiotin (c). 20 μg of eluted proteins were solved by SDS PAGE (b, c). The same amount of eluted proteins was incubated with ribosomal RNAs 1 h at 37 °C and then loaded on 1% bleach agarose gel (d).