Frequency of replacement mutations (black) and silent mutations (white) of each codon of productively rearranged VL genes of B cells isolated from peripheral blood and from the parotid gland of a patient with Sjögren's syndrome. The frequency of mutation of each codon is calculated as the percentage of sequences that contain mutations in particular codon positions. Mutational 'hot spots' of replacement mutations are shown. Nonproductive VL genes were not analyzed because of the small number of mutations. CDR, complementary determining regions.