title: Molecular Characterization of UKp83/68, a Widespread Nuclear Proteins that Bind Poly(A) and Colocalize with a Nuclear Speckle's Component.
abstract: We have cloned a gene from a rat liver cDNA library, representing alternatively spliced cDNAs encoding 83-kDa and 68-kDa proteins, which we have designated as UKp83 and UKp68, respectively. Both proteins have a predicted nuclear localization signal and five CCCH motifs (zinc-binding motifs), and share a degree of sequence similarity with Nab2, a yeast protein that contains nucleic acidbinding motifs and tandem CCCH zinc fingers. Nab2 binds homopolymeric RNA and single-stranded DNA and regulates poly(A) tail length and the export of mRNA to the cytosol. The CCCH motifs of UKp83/68 bound poly(A) and ssDNA strongly and other RNA homopolymers and dsDNA less efficiently. The UKp83/68 protein localized within the nucleus with a fibrous or punctate structure that reflected the distribution of SC35, a known marker of nuclear speckles which are nuclear domains enriched in pre-mRNA splicing factors and located in the interchromatin regions of the nucleoplasm of mammalian cells. The distribution of UKp83/68 changed during the different stages of mitosis. During prometaphase, when the nuclear envelope disintegrates, the protein becomes partially localized on the chromosomes; at other times, transiently dispersed over the cytoplasm with the formation of fibrous structure. The transient expression of UKp83 in HEK293T cells had no apparent effect on cellular function, whereas the expression of an antisense sequence or C-terminal domain of UKp83 induced apoptosis. These results suggest that UKp83/68 is probably essential for cell viability and may play important role in mRNA processing.
authors.affiliation: Department of Cellular and Environmental Biology Graduate School, Tokyo Medical and Dental University 1-5-45 Yushima Bunkyo-ku, Tokyo 113-8510, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Miyakura
authors.affiliation: Department of Cellular and Environmental Biology Graduate School, Tokyo Medical and Dental University 1-5-45 Yushima Bunkyo-ku, Tokyo 113-8510, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Hara
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D029543:Nucleocytoplasmic Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D039102:Poly(A)-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011487:Protein Conformation; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D051381:Rats; D014018:Tissue Distribution; D016335:Zinc Fingers
chemical_list: D018076:DNA, Complementary; D019913:Nuclear Localization Signals; D029543:Nucleocytoplasmic Transport Proteins; D039102:Poly(A)-Binding Proteins; D012333:RNA, Messenger