(A) Cells were treated with or without MMS and were analyzed by immunoblotting using an monoclonal antibody to PCNA. The asterisk denotes a band reactive with PCNA antibodies, possibly corresponding to a PCNA modification independent of K164 and Rad18.
(B) Analysis of clones stably transfected with His-tagged ubiquitin or SUMO-1 expression vectors. Whole cell lysates (left) and lysates after NiNTA chromatography (right) are shown. The positions expected for unmodified, mono-ubiquitinated, and SUMOylated PCNA are indicated by lines. Due to the low residual level of PCNA ubiquitination in the RAD18 mutant, this modification could not be detected by pull-downs. The bands at the bottom represent low levels of unmodified PCNA unspecifically bound to the beads.
(C) Quantification of mono-ubiquitinated and SUMOylated PCNA, histone H3, and AID by immunoblotting. Cells were treated with or without MMS, and immunoblotted using monoclonal antibodies to PCNA (left upper), histone H3 (left middle), and AID (left lower). The values for mono-ubiquitinated and SUMOylated PCNA given in the right hand graphs were calculated as described in the Materials and Methods.

(A) FACS profiles of representative subclones derived from a sIgM (+) cell after staining with a monoclonal antibody to IgM. (B) The average percentages of events falling into sIgM (−) gates based on the measurement of 24 subclones are shown by graph.

(A) Frequencies of particular nucleotide substitutions within light-chain gene. (B) A graphical view showing the frequencies of different types of mutations per hundred sequences.

(A) Alignment of the human, mouse, chicken, Schizosaccharomyces pombe, and S. cerevisiae PCNA amino acid sequences. Amino acid 164 serving as the attachment site for ubiquitination in S. cerevisiae is marked by an asterisk.
(B) A physical map of the PCNA locus and the PCNA mutagenesis construct, pPcna^K164RBsr. The targeting strategy of PCNA locus and the genealogy of the mutant clones are shown below and to the right, respectively.
(C) Sequence chromatographs covering the PCNA codon 164 which was changed from AAA in the AID^RψV⁻ clone to AGA in the PCNA^K164R/K164R clone.

The values of DNA damaging agents, which give 10% cell viability, are also summarized (D₁₀ values).

Ig light-chain sequence variation in the PCNA^K164R/K164R clone. All sequence differences in the region from the first intron to the J-C intron are shown relative to the rearranged light-chain consensus sequence of the AID^RψV⁻ precursor clone. The position of complementary determining regions CDR1, CDR2, and CDR3 and that of Jλ are indicated.