Fig. 3. Correlation of SBS9 with genomic attributes and timing of mutational processes.

a, Mutational spectra of the SBS9 and SHM signatures. Trinucleotide contexts on the x-axis represent 16 bars within each substitution class, divided into 4 sets of 4 bars, grouped by the nucleotide 5′ to the mutated base, and within each group by the 3′ nucleotide. The y-axis shows the number of mutations in each class. b, The number of SBS9 mutations genome-wide and the percentage of bases in IGHV that are mutated in the productive rearrangement of memory B cells. The line represents the linear regression estimate of the correlation. c, Number of SBS9 mutations versus telomere length per genome, coloured by cell type. The regression line is for memory B cells. d, Explanatory power of each significant genomic feature in the generalized additive model (GAM), expressed as the R² of the individual GAM for predicting number of SBS9 mutations (left) or number of SBSblood or SBS1 mutations (right) per 10-kb window. LAD, lamina-associated domain. e, Performance of prediction of genome-wide mutational distribution attributable to particular mutational signatures from histone marks of 149 epigenomes representing distinct blood cell types and different phases of development (numbers after cell types on y-axis indicate replicates); ticks are coloured according to the epigenetic cell type (purple, HSC; blue, naive B cell; grey, memory B cell; maroon, GC B cell); black points depict values from tenfold cross-validation; P-values for comparison of the tenfold cross-validation values by two-sided Wilcoxon test. CS, class switched; GC, germinal centre; HSC, hematopoietic stem cell; Mem, memory; Mega, megakaryocyte.