Mismatch repair deficient human cells: spontaneous and MNNG-induced mutational spectra in the HPRT gene

Mutat Res. 2000 May 30;450(1-2):125-38. doi: 10.1016/s0027-5107(00)00020-8.


We have determined both the spontaneous and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced mutational spectra in the HPRT gene of human cells (MT1) defective in the mismatch repair gene hMSH6 (GTBP). Eight of nine exons and nine of sixteen intronic flanking sequences were scanned, encompassing >900 bp of the HPRT gene. Mutant hotspots were detected and separated by differences in their melting temperatures using constant denaturant capillary electrophoresis (CDCE) or denaturing gradient gel electrophoresis (DGGE).A key finding of this work is that a high proportion of all HPRT inactivating mutations is represented by a small number of hotspots distributed over the exons and mRNA splice sites. Thirteen spontaneous hotspots and sixteen MNNG-induced hotspots accounted for 55% and 48% of all 6TG(R) point mutations, respectively. MNNG-induced hotspots were predominantly G:C-->A:T transitions. The spontaneous spectrum of cells deficient in hMSH6 contained transversions (A:T-->T:A, G:C-->T:A, A:T-->C:G), transitions (A:T-->G:C), a plus-one insertion, and a minus-one deletion. Curiously, G:C-->A:T transitions, which dominate human germinal and somatic point mutations were absent from the spontaneous hMSH6 spectra.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alkylating Agents / toxicity
  • Base Pair Mismatch*
  • Base Sequence
  • Cell Line
  • DNA Primers / genetics
  • DNA Repair / genetics*
  • DNA-Binding Proteins / genetics
  • Humans
  • Hypoxanthine Phosphoribosyltransferase / genetics*
  • Methylnitronitrosoguanidine / toxicity*
  • Mutation*
  • Polymerase Chain Reaction


  • Alkylating Agents
  • DNA Primers
  • DNA-Binding Proteins
  • G-T mismatch-binding protein
  • Methylnitronitrosoguanidine
  • Hypoxanthine Phosphoribosyltransferase