NUCLEIC-ACID BINDING AND INTRACELLULAR-LOCALIZATION OF UNR, A PROTEINWITH 5 COLD SHOCK DOMAINS

The unr gene was identified as a transcription unit located immediatel y upstream of N-ras in the genome of several mammalian species. While this genetic organization could be important for the transcriptional r egulation of unr and N-ras, the function of the protein product of unr is unknown. unr is ubiquitously expressed and codes for an 85 kDa pro tein which is not closely related to previously characterized proteins . Nevertheless, a search for protein motifs has indicated the presence of five 'cold shock domains' within unr, a motif present in procaryot ic cold shock proteins and the vertebrate Y box factors. As these prot eins have been reported to interact with nucleic acids, we investigate d whether unr could bind to some classes of nucleic acids. We report h ere that unr has a high affinity for single-stranded DNA or RNA and a low affinity for double-stranded nucleic acids. Its low affinity for d ouble-stranded NDA clearly distinguishes unr has only a low affinity f or most simple polymers including polyA stretches. unr is also charact erized by its low affinity for double-stranded and structured RNAs. We further determined that unr is mostly localized in the cytoplasm and is in part associated with the endoplasmic reticulum. These studies in dicate that unr is a novel single-stranded nucleic acid binding protei n which is likely to be associated with cytoplasmic mRNA in vivo.