Wu C H, Black L W
Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore 21201, USA.
J Mol Biol. 1995 Apr 7;247(4):604-17.
Bacteriophage T4 gene 17 amplification mutants Hp17 that carry two to six tandem repeats of the genes 17-18 region were isolated by growth of gene 17 amber mutants on ochre suppressor strains of Escherichia coli. These mutants arise from an initial sequence-specific recombination between two GCTCA sequences in a 24 bp imperfect homology box in genes 16 and 19. The initial recombination occurred in the wild-type phage T4 population, as shown by polymerase chain reaction, at a frequency of about 10(-6), which is consistent with the frequency of mutant isolation. T4 phage with mutations of the 3rd, 6th, 9th, 12th, or 15th positions in the 24 bp box of gene 16 either failed to produce gene amplification mutant Hp17 or produced gene amplification mutants from an initial recombination at other regions. Among the mutants that failed to produce gene amplification mutants, the initial recombination generally occurred at lower frequencies at either the GCTCA sequence or other sequences. Since the gene amplification mutations are eliminated or shifted to different sequences by base changes that increase as well as decrease homology, the predominant recombination event between the gene 16 and 19 recombination boxes appears to be sequence-dependent rather than homology-dependent.
通过噬菌体T4基因17琥珀突变体在大肠杆菌赭石抑制菌株上生长，分离出携带基因17 - 18区域两到六个串联重复的噬菌体T4基因17扩增突变体Hp17。这些突变体源于基因16和19中24 bp不完全同源框内两个GCTCA序列之间的初始序列特异性重组。如聚合酶链反应所示，初始重组发生在野生型噬菌体T4群体中，频率约为10(-6)，这与突变体分离频率一致。基因16的24 bp框中第3、6、9、12或15位发生突变的T4噬菌体要么无法产生基因扩增突变体Hp17，要么从其他区域的初始重组产生基因扩增突变体。在未能产生基因扩增突变体的突变体中，初始重组通常在GCTCA序列或其他序列处发生的频率较低。由于基因扩增突变通过增加和降低同源性的碱基变化被消除或转移到不同序列，基因16和19重组框之间的主要重组事件似乎是序列依赖性的，而不是同源性依赖性的。
