Center M S
J Virol. 1972 Jul;10(1):115-23. doi: 10.1128/JVI.10.1.115-123.1972.
After infection with bacteriophage T7, parental and newly synthesized deoxyribonucleic acid (DNA) exhibit an extremely fast sedimentation rate in neutral sucrose gradients. This fast-sedimenting component (intermediate I) has a sedimentation constant of about 1,500S and contains T7 DNA as determined by DNA-DNA hybridization experiments. Pulse-chase experiments indicate that the fast-sedimenting material is metabolically active and serves as a precursor to the formation of T7 DNA. Intermediate I contains about 2.5 to 7% of the total (3)H-labeled protein formed between 3 and 9.5 min after T7 infection. Treatment of intermediate I with Pronase results in the release of the DNA from the complex. At early times after infection, a second intermediate (intermediate II) can be detected which contains both parental and newly synthesized DNA sedimenting slower than intermediate I but 2 to 3 times as fast as mature T7 DNA. Intermediates I and II containing parental DNA are formed after infection of the nonpermissive host with an amber mutant in gene 1, a gene whose expression is necessary for the synthesis of most T7 proteins. The two intermediates are also observed when infection with T7 wild type is carried out in the presence of chloramphenicol.
用噬菌体T7感染后，亲本和新合成的脱氧核糖核酸（DNA）在中性蔗糖梯度中呈现出极快的沉降速率。这种快速沉降成分（中间体I）的沉降常数约为1500S，通过DNA-DNA杂交实验确定其含有T7 DNA。脉冲追踪实验表明，这种快速沉降物质具有代谢活性，并作为T7 DNA形成的前体。中间体I含有在T7感染后3至9.5分钟之间形成的总（3）H标记蛋白质的约2.5%至7%。用链霉蛋白酶处理中间体I会导致DNA从复合物中释放出来。在感染后的早期，可以检测到第二种中间体（中间体II），其含有亲本和新合成的DNA，沉降速度比中间体I慢，但比成熟的T7 DNA快2至3倍。在基因1中携带琥珀突变体的非允许宿主被感染后，会形成含有亲本DNA的中间体I和II，基因1的表达对于大多数T7蛋白质的合成是必需的。当在氯霉素存在下用T7野生型进行感染时，也会观察到这两种中间体。
