A PROFLAVIN-INDUCED FRAMESHIFT HOTSPOT IN THE THYMIDYLATE SYNTHASE GENE OF BACTERIOPHAGE-T4

被引:12
作者
BROWN, MD
RIPLEY, LS
HALL, DH
机构
[1] GEORGIA INST TECHNOL,SCH BIOL,ATLANTA,GA 30332
[2] UNIV MED & DENT NEW JERSEY,NEW JERSEY MED SCH,DEPT MICROBIOL & MOLEC GENET,NEWARK,NJ 07103
来源
MUTATION RESEARCH | 1993年 / 286卷 / 02期
关键词
HOTSPOT; MUTAGENIC; PROFLAVIN; TOPOISOMERASE-II; BACTERIOPHAGE-T4; THYMIDYLATE SYNTHASE GENE;
D O I
10.1016/0027-5107(93)90183-G
中图分类号
Q3 [遗传学];
学科分类号
071007 ; 090102 ;
摘要
Twenty-one independent thymidylate synthase deficient (td) mutants were isolated after proflavin mutagenesis of T4Do phage. A strikingly high proportion of these mutations (17 of 21; 80%) mapped in a small 122 nucleotide (nt) region which spans the 5' splice site of this intron-containing gene. This region comprises only 14% of the total td exon sequence. RNA sequence analysis of these mutants identified a series of frameshift insertion/deletion mutations and indicated a hotspot for proflavin-induced mutations in the 3' end of exon I of the td gene. The mutant sequences at the hotspot site fully support a previously proposed mutagenic mechanism for proflavin-induced mutations in which frameshifts are produced as a consequence of exonuclease or DNA polymerase activity at the 3' ends of nicks in the DNA produced by perturbation of the T4-encoded type II topoisomerase activity by the acridine. Sixteen of the seventeen DNA mutations in the hotspot region can be explained by the model as a consequence of enzymatic processing of nicks at two phosphodiester bonds staggered by 4 base pairs (bp) and located on opposite strands of the DNA. Thus, these mutants exhibit precisely the symmetry expected of topoisomerase-mediated mutagenesis. The DNA sequences of the td hotspot mutants, when considered with the sequences of proflavin-induced mutants in the T4 rIIB and lysozyme genes, confirm the view that proflavin-induced mutations in diverse bacteriophage T4 DNA sequences are all produced by the topoisomerase-dependent mechanisms and do not support the view that classical misalignments in DNA repeats are hotspots for proflavin-induced mutagenesis in T4.
引用
收藏
页码:189 / 197
页数:9
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