C. Enenkel et al., IDENTIFICATION OF A YEAST KARYOPHERIN HETERODIMER THAT TARGETS IMPORTSUBSTRATE TO MAMMALIAN NUCLEAR-PORE COMPLEXES, The Journal of biological chemistry, 270(28), 1995, pp. 16499-16502
Targeting of import substrate to nuclear pore complexes of permeabiliz
ed vertebrate cells was previously shown to require a protein complex
composed of two subunits, termed karyopherin. Yeast contain a homologu
e of karyopherin alpha named Srp1p, which was initially identified as
a genetic Suppressor of mutations in a subunit of RNA polymerase I. To
determine whether yeast contain a karyopherin complex that includes S
rp1p as the karyopherin alpha homologue, we genetically replaced Srp1p
with a Srp1-Protein A chimera, Cytosol from this strain contained a c
omplex, composed of the chimera and a protein of 95 kDa, that was puri
fied using affinity chromatography on IgG Sepharose, Microsequence ana
lysis showed that the 95-kDa protein was identical with a yeast protei
n encoded by gene L8300.15 on chromosome XII. Sequence comparison reve
aled that the L8300.15 gene product is the closest structural homologu
e of vertebrate karyopherin beta. The yeast alpha and beta karyopherin
subunits were expressed in Escherichia coli and were purified, When c
ombined, they formed a heterodimeric complex and were active in target
ing import substrate to nuclear envelopes of mammalian cells. We propo
se that all karyopherins function as alpha/beta heterodimers.