Table 3.

Characterization of exon 4 p53 mutations in progeny of human B clones following TI activation with/without supplementary PGE₂

Mutation type	Mutations [sites (total possible sites)]		Mutation frequency		P
	No pulse	+PGE2	No pulse	+PGE2
At G	1 (705)	1 (2397)	0.00142	0.00042	0.403
At C	4 (1170)	2 (3978)	0.00342	0.00050	0.027*
At A	0 (540)	2 (1836)	0	0.00109	1
At T	0 (570)	2 (1938)	0	0.00103	1
Sum: G/C	5 (1875)	3 (6375)	0.00267	0.00047	0.018*
Sum: A/T	0 (1110)	4 (3774)	0	0.00106	0.580
Total transitions	4 (2985)	6 (10,149)	0.00134	0.00059	0.249
Total transversions	1 (2985)	1 (10,149)	0.00034	0.00010	0.403
Total SYC/GRS (cold spot)a	2 (630)	2 (2142)	0.00460	0.00135	0.224
Total RGYW/WRCY (hot spot)a	0 (255)	0 (867)	0	0	NA
Total WA	0 (150)	1 (510)	0	0.00196	1
Total TW	0 (150)	0 (510)	0	0	NA
Total MHTa	0 (255)	2 (867)	0	0.00231	1

Comparative analysis of all p53 sequences from single cells of nonpulsed and PGE₂-pulsed cultures derived from 6 diverse donors was performed with the web-based SHMTool (http://scb.aecom.yu.edu/shmtool). This permits determinations of the frequency of various categories of somatic hypermutation on the basis of the base composition and total potential sites of each category available for mutation. For the above comparisons, a stretch of 199 exon 4 p53 residues that were commonly sequenced in all experiments was used. While the low frequency of mutations did not meet the minimal conditions for statistical reliability using the program's χ² analysis, a separate statistical comparison was made with Fisher's exact test.

^aLetter designations for alternate nucleotides: R = A/G; S = G/C; Y = C/T; W = A/T; M = A/C; H = A/C/T (61, 65).

^*P < 0.05 for mutation frequency in pulsed vs. nonpulsed cohort; Fisher's exact test.