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Two major types
of signals have been identified for the
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nuclear import of
proteins: SV40 type and bipartite
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type. The
former was first found in the large T antigen of
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the SV40
virus. It has the following sequence
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PKKKRKV
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This type of
signal is characterized by a few consecutive
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basic residues
and in many cases also contains a proline
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residue.
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The bipartite
type was first identified in Xenopus
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nucleoplasmin
with the following NLS:
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KRPAATKKAGQAKKKK
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Its
characteristic pattern is: two basic residues, 10
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spacer residues,
and another basic region consisting of
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at least 3 basic
residues out of 5 residues.
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