SL1 was discovered by Robert Tjian and his colleagues in 1985 when they separated a HeLa cell extract into two functional fractions.[3] One factor has RNA polymerase I activity, but no ability to initiate accurate transcription of a human rRNA template. This transcription factor, SL1, showed species specificity.[4] That is, it could distinguish between the human and mouse rRNA promoter,[5] and added increasing amount of human template at the expense of the mice template.[6] Tijian and coworkers went on to show that by footprinting a partially purified polymerase 1 preparation could bind to the human rRNA promoter. In particular it causes a footprint over a region of the UCE called A site.[7] This binding is not due to polymerase I itself but to a transcription factor called upstream binding factor, UBF.
Function
SLI functions in assembling the transcription preinitiation complex. It is also a major determinant of species-specificity in ribosomal RNA gene transcription. Research suggests that UBF and SL1 act synergistically to stimulate transcription. Recent investigation also suggests that SL1 is a target for cancer therapy.[8]
Structure
SL1 is composed of the TATA-binding protein and at least four TAF (TATA box-binding protein-associated factor) subunits (TAF1A, TAF1B,TAF1C and TAF1D).[9] It is therefore possible to inhibit SL1 activity with anti-TBP antibodies.
