# Structures and Mechanisms of Nuclear Import and Export

> **NIH NIH R01** · UT SOUTHWESTERN MEDICAL CENTER · 2020 · $16,031

## Abstract

Abstract of grant 5 R01 GM069909-17: Karyopherin-
protein transport between the nucleus and the cytoplasm. Of the 20 Kaps in human cells, 11 are
import-Kaps or Importins, each recognizing a distinct set of protein cargos. This proposal
describes structural, biochemical and biophysical analyses of nuclear import systems for core
histones H2A/H2B and H3/H4. Here, we propose to understand how histones H2A/H2B are
recognized by their primary human importer Importin-9 (Imp9) and by the homologous yeast
Kap114. We will determine the mechanisms of how H2A/H2B is recognized by the Importins,
how the GTPaseRan interacts with the Importin-H2A/H2B complex and how histone chaperones
affect these interactions. We will also study how histones H3/H4 are recognized by their primary
human importer,Importin-4 (Imp4). We will explain how histone chaperone Asf1 contributes to
nuclear import of H3/H4 and how RanGTP regulates these multi-protein complexes
Specific aims: Aim 2 seeks to determine structures of Kap114•H2A-H2B, Kap114•RanGTP,
Kap114•Nap1 and Kap114•H2A-H2B-Nap1 complexes, and analyze the thermodynamics of their
interactions. We have performed much of the biochemical and biophysical analyses, but
crystallographic efforts stalled due to complexes dissociating in crystals and low resolution
crystals. We have had success with cryo-EM (described below), which require new
computational infrastructure to complete the work. Aim 3 seeks to solve structures of the
Imp4•H3-H4•Asf1 complex. Low resolution crystals have been problematic. Cryo-EM success in
Aim 2 suggests that the method should be used with Imp4•H3-H4•Asf1. This Aim will benefit
from cryo-EM computational infrastructure in the lab. Aims 1 and 4 have been completed.

## Key facts

- **NIH application ID:** 10155360
- **Project number:** 3R01GM069909-17S1
- **Recipient organization:** UT SOUTHWESTERN MEDICAL CENTER
- **Principal Investigator:** Yuh Min Chook
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $16,031
- **Award type:** 3
- **Project period:** 2004-02-01 → 2022-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10155360

## Citation

> US National Institutes of Health, RePORTER application 10155360, Structures and Mechanisms of Nuclear Import and Export (3R01GM069909-17S1). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10155360. Licensed CC0.

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