Key result
Expression of the hnRNP K protein trans-activates reporter genes with a variety of RNA polymerase II promoters by increasing the level of transcription.
The hnRNP K protein trans-activates reporter genes by increasing transcription levels, providing insight into its role in mRNA biogenesis.
Does not alter clinical practice; leaves open hnRNP K's role in cardiovascular gene regulation.
The function of many of the pre-mRNA-binding proteins in mRNA biogenesis is unclear. We have analyzed the biochemical function of the hnRNP K protein by using a mouse cDNA clone. A previous study indicated that the expression of hnRNP K activates c-myc promoter in transient transfection assays. We show that the expression of hnRNP K results in a trans-activation of a variety of RNA polymerase II promoters. The trans-activation function depends on the sequences of hnRNP K that are also necessary for RNA binding. However, the RNA binding motifs are not sufficient for trans-activation. We could identify a mutant that bound RNA in vitro but was impaired in its ability to trans-activate the reporter genes. The trans-activation was not a result of the stabilization of the reporter mRNA, because hnRNP K increased the steady-state level of the reporter mRNA without altering its decay rate. By doing nuclear run-on assays, we provide evidence that the hnRNP K protein trans-activates the reporter genes by increasing the level of transcription.
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Lee et al. (1996) studied this question. hnRNP K protein expression vs. Control plasmid was evaluated on Reporter gene expression (CAT activity and RNA synthesis). Expression of the hnRNP K protein trans-activates reporter genes with a variety of RNA polymerase II promoters by increasing the level of transcription.
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