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Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành y học dành cho các bạn tham khảo đề tài: Transcriptional control in the prereplicative phase of T4 development | Hinton Virology Journal 2010 7 289 http www.virologyj.eom content 7 1 289 VIROLOGY JOURNAL REVIEW Open Access Transcriptional control in the prereplicative phase of T4 development Deborah M Hinton Abstract Control of transcription is crucial for correct gene expression and orderly development. For many years bacteriophage T4 has provided a simple model system to investigate mechanisms that regulate this process. Development of T4 requires the transcription of early middle and late RNAs. Because T4 does not encode its own RNA polymerase it must redirect the polymerase of its host E. coli to the correct class of genes at the correct time. T4 accomplishes this through the action of phage-encoded factors. Here I review recent studies investigating the transcription of T4 prereplicative genes which are expressed as early and middle transcripts. Early RNAs are generated immediately after infection from T4 promoters that contain excellent recognition sequences for host polymerase. Consequently the early promoters compete extremely well with host promoters for the available polymerase. T4 early promoter activity is further enhanced by the action of the T4 Alt protein a component of the phage head that is injected into E. coli along with the phage DNA. Alt modifies Arg265 on one of the two a subunits of RNA polymerase. Although work with host promoters predicts that this modification should decrease promoter activity transcription from some T4 early promoters increases when RNA polymerase is modified by Alt. Transcription of T4 middle genes begins about 1 minute after infection and proceeds by two pathways 1 extension of early transcripts into downstream middle genes and 2 activation of T4 middle promoters through a process called sigma appropriation. In this activation the T4 co-activator AsiA binds to Region 4 of Ơ70 the specificity subunit of RNA polymerase. This binding dramatically remodels this portion of Ơ70 which then allows the T4 activator MotA to also interact .
