BACTERIOPHAGE-T7 DNA PACKAGING .3. A HAIRPIN END FORMED ON T7 CONCATEMERS MAY BE AN INTERMEDIATE IN THE PROCESSING REACTION
BACTERIOPHAGE-T7 DNA PACKAGING .3. A HAIRPIN END FORMED ON T7 CONCATEMERS MAY BE AN INTERMEDIATE IN THE PROCESSING REACTION
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DOI：
10.1016/s0022-2836(99)80012-6
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发表时间：
1990-12-20
影响因子：
5.6
通讯作者：
HINKLE, DC
中科院分区：
文献类型：
--
作者：
CHUNG, YB;NARDONE, C;HINKLE, DC
在从 T7 感染细胞中分离的噬菌体 T7 DNA 上发现了一个不寻常的左端（M 端）。该末端具有“发夹”结构并且形成于以T7的核苷酸39,587为中心的短反向重复序列处，位于T7多联体上形成成熟左端的位点左侧190个碱基对。如果 M 端是由 T7 串联体上的双链切割产生的，我们不会检测到将形成的伴随右端。这表明发夹左端可能是由 DNA 中的单链切割产生的，该单链切割用于引发向右 DNA 合成。 M末端的形成不需要T7基因10、18或19的产物，这些蛋白质对于成熟T7末端的形成是必需的。在感染 T7 基因 3（核酸内切酶）突变体期间，噬菌体 DNA 合成减少，多联体不会加工成一定长度的 DNA 分子，但多联体 DNA 上会形成 M 端和成熟的右端。还发现这两个末端与正常 T7 感染期间形成的大的、快速沉积的多联体相关，而成熟的左端仅存在于单位长度的 T7 DNA 分子上。我们提出，从反向重复序列中的切口产生的发夹末端引发的DNA复制提供了一种在DNA包装之前复制末端重复的机制。包装从分支多联体上成熟右端的形成开始，并且当噬菌体头部被填充时，可能需要 T7 基因 3 核酸内切酶来修剪 DNA 上的复制叉。通过去除 190 个碱基对发夹末端以产生成熟的左端来完成多联体加工。
An unusual left end (M-end) has been identified on bacteriophage T7 DNA isolated from T7-infected cells. This end has a "hairpin" structure and is formed at a short inverted repeat sequence centered around nucleotide 39,587 of T7, 190 base-pairs to the left of the site where a mature left end is fomed on the T7 concatemer. We do not detect the companion right end that would be formed if the M-end is produced by a double-stranded cut on the T7 concatemer. This suggests that the hairpin left end may be generated from a single-stranded cut in the DNA that is used to prime rightward DNA synthesis. The formation of M-end does not require the products of T7 genes 10, 18 or 19, proteins that are essential for the formation of mature T7 ends. During infection with a T7 gene 3 (endonuclease) mutant, phage DNA synthesis is reduced and the concatemers are not processed into until length DNA molecules, but both M-end and the mature right end are formed on the concatemer DNA. These two ends are also found associated with the large, rapidly sedimenting concatemers formed during a normal T7 infection while the mature left end is present only on unit length T7 DNA molecules. We propose that DNA replication primed from the hairpin end produced by a nick in the inverted repeat sequence provides a mechanism to duplicate the terminal repeat before DNA packaging. Packaging is initiated with the formation of a mature right end on the branched concatemer and, as the phage head is filled, the T7 gene 3 endonuclease maybe required to trim the replication forks from the DNA. Concatemer processing is completed by the removal of the 190 base-pair hairpin end to produce the mature left end.