Identification of two forms of the RNA polymerase I transcription factor UBF.
AUTOR(ES)
O'Mahony, D J
RESUMO
The structure of the rat homologue of the RNA polymerase I transcription factor UBF was investigated. The sequence of the protein was deduced from the sequence of overlapping cDNAs isolated from a cDNA library and from clones of the products generated by the polymerase chain reaction from random-primed, first-strand cDNA. The sequences of these clones indicated that there were two mRNAs for UBF and that the encoded proteins were similar but not identical. One form of rat UBF was essentially identical to human UBF. The second class of UBF mRNA contained an in-frame "deletion" in the coding region that results in the deletion of 37 amino acids from the predicted protein sequence. This deletion reduces the predicted molecular size of the encoded form of UBF by approximately 4400 from 89.4 kDa to 85 kDa and significantly alters the structure of one of the four HMG-1 homology regions (HMG box-2) in that form of UBF. Evidence for the existence of two mRNAs in rat cells was confirmed by a probe protection assay, and we provide evidence that other vertebrate cells contain these same two forms of UBF mRNA. These results are consistent with the observation that UBF purified from four different vertebrates migrates as two bands upon SDS/PAGE. It has been hypothesized that the HMG motifs are the DNA-binding domains of UBF. Altering one of these "boxes," as in the second form of UBF, may alter the functional characteristics of the transcription factor. Thus, the existence of different forms of UBF may have important ramifications for transcription by RNA polymerase I.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=51409Documentos Relacionados
- HMG box 4 is the principal determinant of species specificity in the RNA polymerase I transcription factor UBF.
- Activation of mammalian ribosomal gene transcription requires phosphorylation of the nucleolar transcription factor UBF.
- The RNA polymerase I transcription factor xUBF contains 5 tandemly repeated HMG homology boxes.
- RNA polymerase I associated factor 53 binds to the nucleolar transcription factor UBF and functions in specific rDNA transcription.
- The HMG box-containing nucleolar transcription factor UBF interacts with a specific subunit of RNA polymerase I.