分子生物学2课件1.pptVIP

Fully functional and species-specific SL1 can be reconstituted from these purified components. TAFIs and TAFIIs could compete with each other for binding to TBP. This finding suggested that the binding of one set of TAFs to TBP is mutually exclusive of binding of the other set. The TBP is identical in the two factors but the TAFs are completely different. These TAFs are completely different from those found in TFIID. 2) Upstream-Binding Factor-UBF This transcription factor is an assembly factor that helps SL1 to bind to the core promoter element. The factor was composed of two polypeptides, of 97 and 94 kD. However, the 97-kD polypeptide alone is sufficient for UBF activity. It works by bending the DNA dramatically. Degree of reliance on UBF varies considerably from one organism to another. Interaction of UBF and SL1 with the hrRNA promoter: SL1 caused no footprint on its own, but enhanced and extended the footprint of UBF in both the UPE and the core element. This enhancement is especially evident in the absence of polymerase I (DNase footprinting) Activation of transcription from the rRNA promoter by SL1 and UBF: SL1 was required for at least basal activity, but UBF enhanced this activity on both templates. UBF is a transcription factor that can stimulate transcription by binding to the UPE, but it can also exert an effect in the absence of the UPE, presumably by binding to the core element. Science 241(1988):1194 Without UPE 3 Class III Factors In 1980 a transcription factor, TFIIIA, was found that bound to the internal promoter of the 5S rRNA gene and stimulated its transcription. Since then, two other transcription factors TFIIIB and C have been discovered. Transcription of all classical class III genes requires TFIIIB and C, and transcription of the 5S rRNA genes requires these two plus TFIIIA. TFIIIA was the first eukaryotic transcription factor to be discovered First member of the family of DNA-binding proteins that feature a zinc finger to be described