Heterogeneous nuclear ribonucleoprotein K is a transcription factor.


Journal Article

The CT element is a positively acting homopyrimidine tract upstream of the c-myc gene to which the well-characterized transcription factor Spl and heterogeneous nuclear ribonucleoprotein (hnRNP) K, a less well-characterized protein associated with hnRNP complexes, have previously been shown to bind. The present work demonstrates that both of these molecules contribute to CT element-activated transcription in vitro. The pyrimidine-rich strand of the CT element both bound to hnRNP K and competitively inhibited transcription in vitro, suggesting a role for hnRNP K in activating transcription through this single-stranded sequence. Direct addition of recombinant hnRNP K to reaction mixtures programmed with templates bearing single-stranded CT elements increased specific RNA synthesis. If hnRNP K is a transcription factor, then interactions with the RNA polymerase II transcription apparatus are predicted. Affinity columns charged with recombinant hnRNP K specifically bind a component(s) necessary for transcription activation. The depleted factors were biochemically complemented by a crude TFIID phosphocellulose fraction, indicating that hnRNP K might interact with the TATA-binding protein (TBP)-TBP-associated factor complex. Coimmunoprecipitation of a complex formed in vivo between hnRNP K and epitope-tagged TBP as well as binding in vitro between recombinant proteins demonstrated a protein-protein interaction between TBP and hnRNP K. Furthermore, when the two proteins were overexpressed in vivo, transcription from a CT element-dependent reporter was synergistically activated. These data indicate that hnRNP K binds to a specific cis element, interacts with the RNA polymerase II transcription machinery, and stimulates transcription and thus has all of the properties of a transcription factor.

Full Text

Cited Authors

  • Michelotti, EF; Michelotti, GA; Aronsohn, AI; Levens, D

Published Date

  • May 1996

Published In

Volume / Issue

  • 16 / 5

Start / End Page

  • 2350 - 2360

PubMed ID

  • 8628302

Pubmed Central ID

  • 8628302

Electronic International Standard Serial Number (EISSN)

  • 1098-5549

International Standard Serial Number (ISSN)

  • 0270-7306

Digital Object Identifier (DOI)

  • 10.1128/mcb.16.5.2350


  • eng