|
Table 2. Pattern of mutations of pS189 rescued from unexposed or MNNG-exposed NHOK, HOK-16B, HOK-18A, and SCC-4 cells*.
|
Type of |
Mutation showing altered gel mobility |
||
|
Cells |
Point mutation |
Deletions
|
Complex mutations |
|
NHOK |
|||
|
S (n=8) |
0 | 0 | 8 (100%) |
|
M (n=25) |
1 (4%) | 0 | 24 (96%) |
|
HOK-16B |
|||
|
S (n=50) |
1 (2%) | 2 (4%) | 47 (94%) |
|
M (n=50) |
8 (16%) | 4 (8%) | 38 (76%) |
|
HOK-18A |
|||
|
S (n=50) |
1 (2%) | 1 (2%) | 48 (96%) |
|
M (n=50) |
5 (10%) | 1 (2%) | 44 (88%) |
|
SCC-4 |
|||
|
S (n=50) |
2 (4%) | 2 (4%) | 46 (92%) |
|
M (n=50) |
9 (18%) | 8 (16%) | 33 (66%) |
S: spontaneous mutations
M: MNNG-induced mutations
To analyze the nature of spontaneous and MNNG-induced mutations in these various cell types, the plasmids were recovered from white and light-blue bacterial colonies and classified as point or complex mutations. The patterns of EcoRI/BamHI double digested fragments were compared with those of wt pS189 fragments. The fragment containing intact supF sequence is 850 base pairs in the absence of insertion or deletion. When mutant plasmids showed an identical digestion pattern with wt pS189, the mutants were classified as point mutation, while mutant plasmids showing different EcoRI/BamHI digestion pattern were classified as plasmids with altered gel mobility. Among altered gel mobility, plasmids showing an identical pattern except shorter supF fragment were classified as deletion, and plasmids which were not included in the above categories were classified as complex mutations. Mutant plasmids classified as point mutation and deletion were also confirmed by nucleotide sequencing as shown in Table 3.
*published in Shin et al., 1996.