Expression of horizontally transferred gene clusters: activation by promoter-generating mutations.
The occurrence of promoter-generating mutations allowing the transcription of heterologous genes has been studied in a system based on the plasmid-mediated conjugal transfer of histidine biosynthetic genes from a donor bacterium (Azospirillum brasilense) into a heterologous Escherichia coli mutant population lacking histidine biosynthetic ability and initially unable to recognize the transcriptional signal of the introgressed gene(s). Under selective stressful conditions, His+ revertants accumulated in the E. coli His- culture. The number of His+ colonies was dependent on the time of incubation under selective conditions, the strength of selective pressure, and on the crowding of cells plated; moreover, it was independent of the physiological status of the cell (i.e. the growth phase). Sequence analysis of plasmid DNA extracted from E. coli His+ revertants revealed that single base substitutions in the region upstream of the A. brasilense his operon resulted in an adjustment of the pre-existing sequence that was rendered similar to the E. coli -10 promoter sequence and transcriptable by the host RNA-polymerase. One particular transition (C --> T) was predominant in the His+ revertants. Data presented here indicated that the barriers to the expression of horizontally transferred heterologous genes or operons may be overcome in a short time scale and at high frequency, and supported the selfish operon model on the origin and evolution of gene clusters.
Dabizzi
S
S
Dipartimento di Biologia Animale e Genetica, Università di Firenze, Florence, Italy.
Ammannato
S
S
Fani
R
R
D019747:Aldose-Ketose Isomerases / Q000096:biosynthesis / Q000235:genetics; D000619:Aminohydrolases / Q000096:biosynthesis / Q000235:genetics; D015806:Azospirillum brasilense / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000032:analysis; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics*; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D005816:Genetic Complementation Test; D006639:Histidine / Q000096:biosynthesis; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes; D005810:Multigene Family / Q000235:genetics*; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D016133:Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid
D001426:Bacterial Proteins; C088157:HisB protein, Salmonella typhimurium; D009097:Multienzyme Complexes; D006639:Histidine; D015500:Chloramphenicol O-Acetyltransferase; C087227:imidazole glycerol phosphate synthase; D000619:Aminohydrolases; D019747:Aldose-Ketose Isomerases; C079656:Phosphoribosyl-5-amino-1-phosphoribosyl-4-imidazolecarboxiamide isomerase