I. Vanseuningen et al., DESCRIPTION OF AN IL-1-RESPONSIVE KINASE THAT PHOSPHORYLATES THE K-PROTEIN - ENHANCEMENT OF PHOSPHORYLATION BY SELECTIVE DNA AND RNA MOTIFS, Biochemistry, 34(16), 1995, pp. 5644-5650
The K protein was first identified in the heterogeneous ribonucleoprot
ein particle (hnRNP). Subsequently, K protein was shown to bind sequen
ce-specific single- and double-stranded DNA, stimulate transcription,
and bind Src, Fyn, Lyn, and Vav via SH3 interactions. The K protein al
so binds to the KB enhancer motif which stimulates its phosphorylation
in vitro by an associated serine/threonine kinase. To gain more insig
ht into this unique nucleic acid-dependent phosphorylation process, we
set out to examine the regulation of this kinase. We demonstrate that
the K protein exists in a complex with an IL-1-responsive kinase and
that phosphorylation of the K protein by this kinase is augmented by e
ither cognate DNA or RNA sequences. The IL-1-responsive kinase activit
y associated with the K protein is reduced by phosphatase treatment, s
uggesting that the K protein kinase activity is regulated by phosphory
lation. The observation that phosphorylation of the K protein is DNA-
or RNA-dependent and IL-1-responsive suggests that the function of the
K protein is tightly regulated.