Different structures of selected and unselected araB-lacZ fusions.
Formation of araB-lacZ coding-sequence fusions is a key adaptive mutation system. Eighty-four independent araB-lacZ fusions were sequenced. All fusions carried rearranged MuR linker sequences between the araB and lacZ domains indicating that they arose from the standard intermediate of the well-characterized Mu DNA rearrangement process, the strand transfer complex (STC). Five non-standard araB-lacZ fusions isolated after indirect sib selection had novel structures containing back-to-back inverted MuR linkers. The observation that different isolation procedures gave rise to standard and non-standard fusions indicates that cellular physiology can influence late steps in the multi-step biochemical sequence leading to araB-lacZ fusions. Each araB-lacZ fusion contained two novel of DNA junctions. The MuR-lacZ junctions showed 'hot-spotting' according to established rules for Mu target selection. The araB-MuR and MuR-MuR junctions all involved exchanges at regions of short sequence homology. More extensive homology between MuR and araB sequences indicates potential STC isomerization a resolvable four-way structure analogous to a Holliday junction. These results highlight the molecular complexity of araB-lacZ fusion formation, which may be thought of as a multi-step cell biology process rather than a unitary biochemical reaction.
Maenhaut-Michel
G
G
Université Libre de Bruxelles, Department of Molecular Biology, Rhode-St-Genése, Belgium.
Blake
C E
CE
Leach
D R
DR
Shapiro
J A
JA
D010583:Bacteriophage mu / Q000235:genetics; D001483:Base Sequence; D003001:Cloning, Molecular; D004252:DNA Mutational Analysis; D004926:Escherichia coli / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics*; D005809:Genes, Regulator; D007763:Lac Operon / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D012641:Selection, Genetic; D012689:Sequence Homology, Nucleic Acid; D001616:beta-Galactosidase / Q000235:genetics*
D001616:beta-Galactosidase