Identification of two HSP70-related Xenopus oocyte proteins that are capable of recycling across the nuclear envelope

Journal Article · Thu Nov 01 00:00:00 EST 1990 · Journal of Cell Biology; (USA)

DOI:https://doi.org/10.1083/jcb.111.5.1775· OSTI ID:6172077

Mandell, R B; Feldherr, C M ^[1]

---

1. Univ. of Florida, Gainesville (USA)

Two 70-kD polypeptides, B3 and B4, are present in equivalent concentrations in the nucleus and cytoplasm of Xenopus oocytes. The objectives of this study were to determine if they (a) are members of the 70-kD family of heat shock proteins, and (b) recycle between the nuclear and cytoplasmic compartments. Evidence based on high-affinity binding to ATP, cross-reactivity of B3/B4-specific antibodies with rat hsc70, and a comparison of cyanogen bromide cleavage peptide maps with hsc70, verified that B3 and B4 are members of the 70-kD family of heat-shock proteins. Nuclear uptake studies were performed by microinjecting 125I-labeled B3/B4, rat hsc70, and BSA into the cytoplasm of oocytes, and examining their subsequent intracellular distributions. By 6 h postinjection, the nuclear concentration of B3/B4 and hsc70 were approximately 24-fold greater than BSA controls. It was also found that B3/B4-coated gold particles as large as 120A in diameter were able to enter the nucleus by passing through the pores. Nuclear efflux was analyzed by microinjecting the iodinated proteins directly into the oocyte nuclei. 2 h after nuclear injection, at least 46% of the B3/B4 and 60% of the hsc70 were found in the cytoplasmic fractions, compared with less than 10% for the BSA controls. Cell fusion experiments, in which labeled, anucleate oocyte vegetal hemispheres were fused, under oil, with nucleate unlabeled animal hemispheres, demonstrated that cytoplasmic B3 and B4 could enter the nucleus after equilibration was reached, arguing against the existence of separate nuclear and cytoplasmic populations. Collectively, these results show that B3, B4, and rat hsc70 are transported across the nuclear envelope and recycle between the nucleus and cytoplasm.

• OSTI ID: 6172077
• Journal Information: Journal of Cell Biology; (USA), Vol. 111:5 Pt 1; ISSN 0021-9525
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
POLYPEPTIDES
MEMBRANE TRANSPORT
ALBUMINS
AMINO ACID SEQUENCE
ATP
CELL MEMBRANES
CELL NUCLEI
CYTOPLASM
EGGS
FROGS
IODINE 125
TRACER TECHNIQUES
AMPHIBIANS
ANIMALS
AQUATIC ORGANISMS
BETA DECAY RADIOISOTOPES
CELL CONSTITUENTS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
MEMBRANES
MOLECULAR STRUCTURE
NUCLEI
NUCLEOTIDES
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
PEPTIDES
PROTEINS
RADIOISOTOPES
VERTEBRATES
550201* - Biochemistry- Tracer Techniques