A heterogeneous-nuclear ribonucleoprotein found in the cell nucleus and the cytoplasm. heterogeneous-nuclear ribonucleoprotein k has been implicated in the regulation of gene expression at nearly all levels: GENETIC TRANSCRIPTION; mRNA processing (rna processing, post-transcriptional), mRNA transport, mRNA stability, and translation (TRANSLATION, GENETIC). The hnRNP protein has a strong affinity for polypyrimidine-rich RNA and for single-stranded polypyrimidine-rich dna. Multiple hnRNP K protein isoforms exist due to alternative splicing and display different nucleic-acid-binding properties.