Latent HIV infection of long-lived cells is a barrier to viral clearance. Hematopoietic stem and progenitor cells are a heterogeneous population of cells, some of which are long-lived. CXCR4-tropic HIVs infect a broad range of HSPC subtypes, including hematopoietic stem cells, which are multi-potent and long-lived. However, CCR5-tropic HIV infection is limited to more differentiated progenitor cells with life spans that are less well understood. Consistent with emerging data that restricted progenitor cells can be long-lived, we detected persistent HIV in restricted HSPC populations from optimally treated people. Further, genotypic and phenotypic analysis of amplified env alleles from donor samples indicated that both CXCR4- and CCR5-tropic viruses persisted in HSPCs. RNA profiling confirmed expression of HIV receptor RNA in a pattern that was consistent with in vitro and in vivo results. In addition, we characterized a CD4high HSPC sub-population that was preferentially targeted by a variety of CXCR4- and CCR5-tropic HIVs in vitro. Finally, we present strong evidence that HIV proviral genomes of both tropisms can be transmitted to CD4-negative daughter cells of multiple lineages in vivo. In some cases, the transmitted proviral genomes contained signature deletions that inactivated the virus, eliminating the possibility that coincidental infection explains the results. These data support a model in which both stem and non-stem cell progenitors serve as persistent reservoirs for CXCR4- and CCR5-tropic HIV proviral genomes that can be passed to daughter cells.

HIV genomes can be detected in CD133-sorted cells from a subset of donors with long-term viral suppression and, in most cases, cannot be explained by contamination with CD3(+) T cells.

HMGB proteins are abundant non-histone components of eukaryotic chromatin. The biological function of DNA sequence nonspecific HMGB proteins is obscure. These proteins are composed of one or two conserved HMG box domains, each forming three alpha helices that fold into a sequence nonspecific DNA-binding module recognizing the DNA minor groove. Box A and box B homology domains have subtle sequence differences such that box B domains bend DNA strongly while DNA bending by isolated box A domains is weaker. Both box A and box B domains preferentially bind to distorted DNA structures. Here we show using DNA cyclization kinetics assays in vitro and E. coli DNA looping assays in vivo that an isolated HMG box A domain derived from human HMGB2 folds poorly and does not enhance apparent DNA flexibility. Surprisingly, substitution of a small number of cationic residues from the N-terminal leader of a functional yeast box B protein, Nhp6Ap, confers the ability to enhance DNA flexibility. These results demonstrate important roles for cationic leader amino acids in HMGB folding, DNA interaction, and DNA bending.HMGB 1 sequence non-specific DNA binding proteins are abundant non-histone proteins in eukaryotic cells (1-3). These small proteins are composed of one [e.g. S. cerevisiae Nhp6Ap (4-8), D. melanogaster HMG-D (9,10)] or two [e.g. vertebrate HMGB1,, S. cerevisiae Hmo1p (16)] repeats of a conserved ~80-residue "HMG box" motif. Highly charged flanking sequences are also often present (3). Thus, HMGB proteins are a subset of the proteins that carry one or two domains homologous to the ancestral HMG box. HMGB proteins accumulate to greater than micromolar concentrations in eukaryotic cells such that there is approximately one HMGB protein for every 5-10 nucleosomes in chromatin.Among the striking features of HMGB proteins is their ability to induce strong DNA bending and, consequentially, their preference for binding to distorted DNA structures such as cruciforms (11,(16)(17)(18) and chemical lesions (19)(20)(21)(22)(23). DNA bending in these complexes can exceed 90°. In this sense, HMGB proteins are functionally (though not structurally) reminiscent of the prokaryotic nucleoid protein HU (24). There is evidence that HU functions by inducing a flexible hinge in DNA (25,26), and HMGB proteins appear to alter DNA structure through formation of hinges with enhanced flexibility (27)(28)(29).*To whom correspondence should be addressed. Tel: 507-284-9041. Fax: 507-284-2053. E-mail: maher@mayo.edu.. § these co-authors contributed equally to this work 1 Abbreviations: BSA, bovine serum albumin; box A, N-terminal high mobility group homology domain; box B, C-terminal high mobility group homology domain; EDTA, ethylenediaminetetraacetic acid; FACT, facilitator of chromatin transactions; HEPES, (4-(2-hydroxyethyl)-1-piperazineethylsulfonic acid); HMG, high mobility group; HMGB, high mobility group B protein family; HMGB1, mammalian member 1 of HMGB protein family; HMGB2, mammalian member 2 of HMGB protein family; HPLC, high per...