Madsen Peter L, Hammer Karin
Department of Microbiology, Building 301, Technical University of Denmark2800 LyngbyDenmark.
Microbiology (Reading). 1998 Aug;144 ( Pt 8):2203-2215. doi: 10.1099/00221287-144-8-2203.
Transcriptional analysis by Northern blotting identified clusters of early, middle and late transcribed regions of the temperate lactococcal bacteriophage TP901-1 during one-step growth experiments. The latent period was found to be 65 min and the burst size 40 +/- 10. The eight early transcripts, all mapping in a 13 kb region adjacent to the attachment site of TP901-1, were present at maximal levels 10 min after infection. The four middle transcripts, observed at maximal levels 30 min after infection, are all located within a 2 kb region at the distal end of the early transcripts. The late class of transcripts were detected 40 min after infection and the amounts of these transcripts increased with time. The late transcripts were localized to the 13 kb region adjacent to the 2 kb middle transcribed region. The sequence of almost 4 kb of the early region was determined, allowing a detailed transcriptional map for the early region of which in total 6.4 kb was sequenced. Sequence analysis of the early region revealed two closely positioned but divergently orientated promoters, PL and PR, in accordance with the orientation of the ORFs and the transcriptional map. Nine ORFs were found, and similarities to a phage repressor, a single-stranded DNA-binding protein, a topoisomerase, a Cro-like protein and two other phage proteins of unknown function were detected. The gene arrangement in the early transcribed region of TP901-1 thus consists of two transcriptional units: one from PR containing four genes, of which at least two (the integrase gene and putative repressor) are needed for lysogeny, and the divergent and longer transcriptional unit from PL, presumably encoding functions required for the lytic life cycle. ORFs with homology to proteins involved in DNA replication were identified on the latter transcriptional unit.
通过Northern印迹法进行的转录分析确定了温和型乳球菌噬菌体TP901-1在一步生长实验期间的早期、中期和晚期转录区域簇。发现潜伏期为65分钟，爆发量为40±10。八个早期转录本都定位在与TP901-1附着位点相邻的13 kb区域，在感染后10分钟达到最大水平。四个中期转录本在感染后30分钟达到最大水平，均位于早期转录本远端的一个2 kb区域内。晚期转录本在感染后40分钟被检测到，其数量随时间增加。晚期转录本定位在与2 kb中期转录区域相邻的13 kb区域。测定了早期区域近4 kb的序列，从而得到了早期区域的详细转录图谱，该区域总共测序了6.4 kb。早期区域的序列分析揭示了两个紧密相邻但方向相反的启动子PL和PR，这与开放阅读框（ORF）的方向和转录图谱一致。发现了九个ORF，并检测到它们与噬菌体阻遏物、单链DNA结合蛋白、拓扑异构酶、Cro样蛋白以及另外两个功能未知的噬菌体蛋白具有相似性。因此，TP901-1早期转录区域的基因排列由两个转录单元组成：一个来自PR，包含四个基因，其中至少两个（整合酶基因和假定的阻遏物）是溶原性所必需的；另一个来自PL的转录单元方向相反且更长，可能编码裂解生命周期所需的功能。在后一个转录单元上鉴定出了与参与DNA复制的蛋白质具有同源性的ORF。
