Physical properties of DNA in vivo as probed by the length dependence of the lac operator looping process

摘要: Plasmid constructs containing a wild-type (O+) lac operator upstream of an operator-constitutive (Oc) control element exhibit length-dependent, oscillatory pattern repression expression the regulated gene as interoperator spacing is varied from 115 to 177 base pairs (bp). Both length dependence and periodicity are consistent with thermodynamic model involving stable looped complex in which bidentate repressor interacts simultaneously both O+ Oc operators. The distance occurs period approximating helical repeat DNA presumably reflects necessity for proper alignment interacting operators along face DNA. In regime examined, presence enhances between 6-fold 50-fold depending upon phasing. This torsional rigidity vivo that vitro measurements. best fit either 9.0 or 11.7 bp/cycle but not 10.5 bp/cycle. interpreted reflecting average 40-bp region plasmid vivo, suggesting local may differ significantly bp/turn. apparent persistence needed data (aapp) only one-fifth standard value. low value aapp be due part bending induced by catabolite activator protein (CAP) bound its site operators.(ABSTRACT TRUNCATED AT 250 WORDS)