A new experimental system for study on adaptive mutations |
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Authors: | Zhong Lü Aoquan Wang |
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Institution: | (1) Institute of Microbiology, Chinese Academy of Sciences, 100080 Beijing, China |
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Abstract: | A super-repressed mutant of purR (purRS), which encodes a repressor protein controlling expression of purine biosynthetic genes inSalmonella typhimurium, grew very slowly on NCE medium with 10 μg/mL Ade and lactose as sole carbon source (cannot form colonies). However, a phenomenon
of late-arising mutations was observed when purRS mutants were spread on NCE+lactose plates and subjected to a prolonged non-lethal selection. The reconstruction experiments
of revertants showed that the late-arising “lac+” mutants are not slow growing mutants. Statistical analysis indicated that the distribution of late-arising mutants is Poisson
distribution, showing that reversion occurred after plating. The result of co-transductional analysis preliminarily showed
that late-arising mutation occurred at selected genepurR or 16 bp PUR box,cis element of structural genepurD. The above results suggest that the phenomenon of late-arising mutation observed by our system is a result of adaptive mutations
which are different from random mutations. This is the first time to extend target genes at which adaptive mutations could
occur from structural genes involved in carbon metabolism and amino acid biosynthesis totrans regulatory gene coding repressor protein. Our results have provided not only a new proof for generality of adaptive mutations
but also a new system for study on adaptive mutations. |
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Keywords: | adaptive mutations purRs purD-lac |
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