Ty1 retrotransposition inFor Ty1 integration to occur, the VLP or a subparticle preintegration complex (PIC) containing at least IN and Ty1 cDNA must return to and transit the nuclear membrane to access a genomic target. Little is known about how Ty1 elements return to the nucleus. Since the yeast nuclear membrane remains intact throughout the cell cycle (8) and since Ty1 VLPs, which are 60 nm in diameter (20, 38), exceed the 25-nm size limit for active transport of a particle across the nuclear pore complex (for a review, see reference 23), an intact nuclear envelope presents a potential barrier to the Ty1 PIC. This problem is analogous to that of retroviral infection of nondividing cells. Whereas most oncoretroviruses require mitotic nuclear membrane dissolution for infectivity (35, 46), lentiviruses, such as human immunodeficiency virus type 1 (HIV-1) and visna virus, can infect terminally differentiated cells (7,24,34,42,52). Translocation of the HIV-1 PIC across the nuclear membrane appears to require or be augmented by the matrix (MA) protein, which contains a nuclear localization signal (NLS), and the Vpr protein (6,15,36,51).Here, we demonstrate that Ty1 IN enters the yeast nucleus with no requirement for additional Ty1 element-encoded proteins. IN nuclear localization is mediated by a C-terminal NLS.The IN NLS appears to be bipartite but with small basic motifs separated by a large spacer region. Point mutations in the NLS basic motifs block transpositional integration but affect Ty1 cDNA homologous recombination less severely. Intragenic complementation analyses indicate that the Ty1 IN NLS region is functionally separate from the catalytic domain and that Ty1 IN probably functions as a multimer. MATERIALS AND METHODSYeast strains and media. Yeast strains DG1251 (yGS37; MAT␣ ura3-167 trp1-GB his3-⌬200 spt3-101) and DG1286 (yGS38; MAT␣ ura3-167 trp1-GB his3-⌬200 spt3-101 rad52-GB) are isogenic derivatives of strain GRF167 (2, 47). Strain DG531 (MATa ade1-100 ura3-52 leu2-3,2-112 his4-519 spt3-101), an isogenic spt3 derivative of strain BWG1-7A, was used for indirect immunofluorescence (IIF) of pGTy1 due to its property of having dispersed VLPs (20,55). DG1377 is a transformant of RDKY 1293 containing the Ty1 IN expression plasmid pGTy1-IN. All media were prepared as described by Sherman et al. (48).Plasmid constructions. Construction of the pGTy1-IN expression plasmid has been described elsewhere (40). Green fluorescent protein (GFP)-LacZ-IN fusion plasmids contained genes coding for either full-length IN, N-terminal deletions of IN, and/or C-terminal truncations of IN that were generated by PCR (41) by using primers complementary to specific sequences of IN. The GFP-LacZ vector was a gift from P. Silver and contains a GAL1-promoted GFP-LacZ fusion. To fuse the IN gene in frame to lacZ, the vector was digested with SacI, which recognizes a unique site in lacZ, and HindIII, which recognizes a unique site 3Ј of the lacZ open reading frame. In the ligation reaction, this fragment was replaced with a lacZ ...

Production of toxic oxygen metabolites provides a mechanism for microbicidal activity of the neutrophil. The NADPH oxidase enzyme system initiates the production of oxygen metabolites by reducing oxygen to form superoxide anion (O 2 .

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This is the first report of a B19V Genotype 3 detected from a plasma donor located in the United States. Although our data are consistent with recent reports suggesting low incidence for this genotype, they indicate its increasing relevance among blood and plasma donors.

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