SPECTRUM OF SPONTANEOUS MISSENSE MUTATIONS CAUSING CYCLIC AMP-RESISTANCE PHENOTYPES IN CULTURED S49 MOUSE LYMPHOMA-CELLS DIFFERS MARKEDLY FROM THOSE OF MUTATIONS INDUCED BY ALKYLATING MUTAGENS
Kb. Gorman et Ra. Steinberg, SPECTRUM OF SPONTANEOUS MISSENSE MUTATIONS CAUSING CYCLIC AMP-RESISTANCE PHENOTYPES IN CULTURED S49 MOUSE LYMPHOMA-CELLS DIFFERS MARKEDLY FROM THOSE OF MUTATIONS INDUCED BY ALKYLATING MUTAGENS, Somatic cell and molecular genetics, 20(4), 1994, pp. 301-311
Mutants of S49 mouse lymphoma cells resistant to cytolysis by analogs
of cyclic AMP (cAMP) generally have missense mutations in the gene enc
oding the regulatory subunit of cAMP-dependent protein kinase. We have
compared the mutations in 95 spontaneous isolates with those in 60 mu
tagen-induced isolates by sequence analysis of amplified cDNAs. Twenty
-nine single basepair substitutions in 19 codons produced selectable p
henotypes. The spontaneous mutant spectrum was dominated by a CpG tran
sition hotspot in the codon for Arg334. This and other nearby CpG site
s were found to be methylated in genomic S49 cell DNA by restriction e
nzyme analyses. Most of the remaining spontaneous mutants had either G
-C --> C-G or T-A --> G-C transversions, which have been associated wi
th damage caused by oxygen radicals. In contrast, the majority of muta
nts induced with the alkylating mutagens ethyl methanesulfonate (EMS)
and N-methyl-N'-nitro-N-nitrosoguanidine had G-C --> A-T mutations at
non-CpG sites; in addition, EMS induced several A-T --> G-C, A-T --> T
-A, and G-C --> T-A substitutions. A single ICR191-induced mutant anal
yzed had a unique A-T --> G-C lesion. A number of spontaneous and muta
gen-induced isolates had closely linked double or triple substitutions
, and two isolates had tandem triple substitutions.