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.
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