Nagy P D, Bujarski J J
Plant Molecular Biology Center, Northern Illinois University, De Kalb 60115, USA.
J Virol. 1996 Jan;70(1):415-26. doi: 10.1128/JVI.70.1.415-426.1996.
Brome mosaic virus, a tripartite positive-stranded RNA virus of plants, was used for the determination of sequence requirements of imprecise (aberrant) homologous recombination. A 23-nucleotide (nt) region that included a 6-nt UUAAAA sequence (designated the AU sequence) common between wild-type RNA2 and mutant RNA3 supported both precise and imprecise homologous recombination, though the latter occurred with lower frequency. Doubling the length of the 6-nt AU sequence in RNA3 increased the incidence of imprecise crossovers by nearly threefold. Duplication or triplication of the length of the AU sequence in both RNA2 and RNA3 further raised the frequency of imprecise crossovers. The majority of imprecise crosses were located within or close to the extended AU sequence. Imprecise recombinants contained either nucleotide substitutions, nontemplated nucleotides, small deletions, or small sequence duplications within the region of crossovers. Deletion of the AU sequence from the homologous region in RNA3 resulted in the accumulation of only precise homologous recombinants. Our results provide experimental evidence that AU sequences can facilitate the formation of imprecise homologous recombinants. The generation of small additions or deletions can be explained by a misannealing mechanism within the AU sequences, while replicase errors during RNA copying might explain the occurrence of nucleotide substitutions or nontemplated nucleotides.
雀麦花叶病毒是一种植物的三分体正链RNA病毒，被用于确定不精确（异常）同源重组的序列要求。一个23个核苷酸（nt）的区域，其中包括野生型RNA2和突变型RNA3之间共有的一个6 nt的UUAAAA序列（称为AU序列），支持精确和不精确的同源重组，尽管后者发生频率较低。将RNA3中6 nt的AU序列长度加倍，不精确交叉的发生率增加了近三倍。在RNA2和RNA3中，将AU序列长度重复或三倍化，进一步提高了不精确交叉的频率。大多数不精确交叉位于扩展的AU序列内或附近。不精确重组体在交叉区域内包含核苷酸替换、非模板化核苷酸、小缺失或小序列重复。从RNA3的同源区域删除AU序列导致仅积累精确的同源重组体。我们的结果提供了实验证据，表明AU序列可以促进不精确同源重组体的形成。小插入或缺失的产生可以通过AU序列内的错配退火机制来解释，而RNA复制过程中的复制酶错误可能解释核苷酸替换或非模板化核苷酸的出现。
