The importance of using absolute mutant frequencies to compare mutation spectra

Escherichia coli K12 W3110 was treated by extremely low frequency electric field ( ELF EFs) 10min with the field intensity of 100，200，300，400kV/m. The mutant frequency reached 31.2×10 -6 at field intensity of 100kV/m, which was about 26-fold over the background (1.2×10 -6 ) and 12-fold over the controls (2.5×10 -6 ). This result indicated that the ELF EFs could act as an mutagen. The results also show that base pair (bp) substitutions were the main type of ELF EFs induced mutations. Although all types of base pair substitutions were observed, 30% of the bp substitutions were G:C → A:T transitions, 70% of the bp substitutions were A:T→T:A, G:C→T:A, A:T→C:G, G:C→ C:G transversions. When the spontaneous and the ELF EFs exposure group were compared, base-pair substitutions, deletions and additions of the ELF EFs exposure group were significantly increased, and the deletion or the addition of a 5'-TGGC-3' sequence at hot spot was decreased from 82 to 26%. But the remarkable increase in absolute Mutation Frequency (MF) of the deletion or the addition of a 5'-TGGC-3' sequence at hot spot in the ELF EFs exposure group suggested that ELF EFs did induce the mutations of this type. The spectra of our ELF EFs exposure group with increasing G:C to A:T transitions and A:T to T:A transversions indicate that ELF EFs exposure may induce SOS response.

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“…The types of mutations and their absolute MF [14] are given in Table 1 (The spontaneous mutants were from Murata-Kamiya et al [10])…”

Section: B Laci − Mutationsmentioning

confidence: 99%