Gene repression by minimal lac loops in vivo.
Nucleic Acids Res
; 38(22): 8072-82, 2010 Dec.
Article
en En
| MEDLINE
| ID: mdl-21149272
ABSTRACT
The inflexibility of double-stranded DNA with respect to bending and twisting is well established in vitro. Understanding apparent DNA physical properties in vivo is a greater challenge. Here, we exploit repression looping with components of the Escherichia coli lac operon to monitor DNA flexibility in living cells. We create a minimal system for testing the shortest possible DNA repression loops that contain an E. coli promoter, and compare the results to prior experiments. Our data reveal that loop-independent repression occurs for certain tight operator/promoter spacings. When only loop-dependent repression is considered, fits to a thermodynamic model show that DNA twisting limits looping in vivo, although the apparent DNA twist flexibility is 2- to 4-fold higher than in vitro. In contrast, length-dependent resistance to DNA bending is not observed in these experiments, even for the shortest loops constraining <0.4 persistence lengths of DNA. As observed previously for other looping configurations, loss of the nucleoid protein heat unstable (HU) markedly disables DNA looping in vivo. Length-independent DNA bending energy may reflect the activities of architectural proteins and the structure of the DNA topological domain. We suggest that the shortest loops are formed in apical loops rather than along the DNA plectonemic superhelix.
Texto completo:
1
Bases de datos:
MEDLINE
Asunto principal:
ADN Bacteriano
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Regulación Bacteriana de la Expresión Génica
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Escherichia coli
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Operón Lac
Idioma:
En
Revista:
Nucleic Acids Res
Año:
2010
Tipo del documento:
Article
País de afiliación:
Estados Unidos