Figure 4.

Chk1 depletion in DT40 cells affects DNA repair pathways. (A) Mutation frequencies in the VJ-region of the Igλ locus (VJλ) in DT40ΨV⁻ wild-type, Chk1 +/+/−/−, Chk1 rec. and AID −/− cell lines. The total number of sequences analyzed is indicated in the center of the chart, and the number of point mutations per DNA sequence is given in the periphery of the pie chart segments. (B) Pattern of nucleotide substitutions detected in the VJλ-region. Tables in the upper part show numbers of independent mutational events and the lower part gives percentages of total mutations. Below each table, the ratio of transition:transversion substitutions at dC/dG is indicated. Significance analysis: X² test. ***P < 0.001, **P < 0.01, *P < 0.05. (C) Percentage of sIgM⁺ cells determined by FACS in individual subclones of the indicated genotypes in the DT40Cre1 cell line. A logarithmic scale is used for better visualization of differences. P-values are given for comparison of cell clones deriving from the same original population. rec.: reconstituted. sIgM: surface IgM. Significance analysis: Student’s t-test. (D) Sequence analysis of the VJλ-region in representative clones analyzed in (C). GCM: Ig gene conversion events; AM: ambiguous mutations; PM: point mutations; TV: transversion mutations; TS: transition mutations; AT: transversion and transition mutations at dAdT. Significance analysis: X² test. Mutational analysis in (A–D) was performed with two representative subclones of each genotype.