Chloroplast gene expression is primarily controlled during the translation of plastid mRNAs. Translation is regulated in response to a variety of biotic and abiotic factors, and requires a coordinate expression with the nuclear genome. The translational apparatus of chloroplasts is related to that of bacteria, but has adopted novel mechanisms in order to execute the specific roles that this organelle performs within a eukaryotic cell. Accordingly, plastid ribosomes contain a number of chloroplast-unique proteins and domains that may function in translational regulation. Chloroplast translation regulation involves cis-acting RNA elements (located in the mRNA 5' UTR) as well as a set of corresponding trans-acting protein factors. While regulation of chloroplast translation is primarily controlled at the initiation steps through these RNA-protein interactions, elongation steps are also targets for modulating chloroplast gene expression. Translation of chloroplast mRNAs is regulated in response to light, and the molecular mechanisms underlying this response involve changes in the redox state of key elements related to the photosynthetic electron chain, fluctuations of the ADP/ATP ratio and the generation of a proton gradient. Photosynthetic complexes also experience assembly-related autoinhibition of translation to coordinate the expression of different subunits of the same complex. Finally, the localization of all these molecular events among the different chloroplast subcompartments appear to be a crucial component of the regulatory mechanisms of chloroplast gene expression.

Vectors derived from human immunodeficiency virus (HIV) hold promise for efficient gene delivery into human hematopoietic cells. In this study, HIV vectors containing different combinations of cis-acting elements, including the HIV central flap sequence, and the woodchuck posttranscriptional regulatory element (WPRE) in combination with two different promoters, were used to transduce primary human lymphocytes and cord blood CD34+ progenitor cells. The effect of these elements on the transduction efficiency and transgene expression was systematically evaluated. The results demonstrate that with the combination of flap, WPRE sequences, and the promoter derived from spleen focus-forming virus (SFFV), a foreign gene can be efficiently delivered into primary human T lymphocytes and cord blood CD34+ cells. The study establishes the parameters for proper vector design to efficiently deliver foreign genes into human hematopoietic cells.

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Sgs1 is a RecQ family DNA helicase required for genome stability in Saccharomyces cerevisiae whose human homologs BLM, WRN, and RECQL4 are mutated in Bloom's, Werner, and Rothmund Thomson syndromes, respectively. Sgs1 and mismatch repair (MMR) are inhibitors of recombination between similar but divergent (homeologous) DNA sequences. Here we show that SGS1, but not MMR, is critical for suppressing spontaneous, recurring translocations between diverged genes in cells with mutations in the genes encoding the checkpoint proteins Mec3, Rad24, Rad9, or Rfc5, the chromatin assembly factors Cac1 or Asf1, and the DNA helicase Rrm3. The S-phase checkpoint kinase and telomere maintenance factor Tel1, a homolog of the human ataxia telangiectasia (ATM) protein, prevents these translocations, whereas the checkpoint kinase Mec1, a homolog of the human ATM-related protein, and the Rad53 checkpoint kinase are not required. The translocation structures observed suggest involvement of a dicentric intermediate and break-induced replication with multiple cycles of DNA template switching.RecQ-like DNA helicases play important roles in the maintenance of genome stability from bacteria to humans. The only member of the RecQ family of 3Ј to 5Ј DNA helicases in the yeast Saccharomyces cerevisiae is Sgs1. Sgs1 has been implicated in the coordination between DNA replication and recombination, in the regulation of homologous recombination (HR) and the suppression of crossover products during HR, and in S-phase checkpoint activation as well as in transcription (16,26,38,49,61,96). As a consequence, cells that lack Sgs1 display a hyperrecombination phenotype, accumulate extrachromosomal ribosomal DNA (rDNA) circles, frequently missegregate chromosomes during mitosis and meiosis, have modestly increased rates of accumulating gross chromosomal rearrangements (GCRs), are sensitive to agents such as hydroxyurea and methyl-methanesulfonate, and show signs of premature aging (29,58,61,86,100,101,104).To date, five human genes encoding RecQ-like (RECQL) proteins have been identified. Mutations in RECQL2 (WRN) (105), RECQL3 (BLM) (23), and RECQL4 (41, 42) cause three rare, cancer-prone disorders, Werner syndrome (WS), Bloom's syndrome (BS), and a subset of Rothmund Thomson syndrome (Type II RTS) (97), respectively, while defects in RECQL1 (73, 74) and RECQL5 (41) have not been linked to a disease. Besides short stature, early onset of diabetes mellitus, and immunodeficiency, BS is characterized by extreme cancer risk, which has been estimated to be 150 to 300 times higher than the risk of malignancy in the unaffected population; in 168 BS patients, 100 cancers of many types had arisen at a mean age of 24.7 years, with many of the patients suffering from multiple primary cancers (31). Although WS patients share some of these symptoms, including early onset of diabetes mellitus and increased cancer susceptibility, they also show numerous other signs of accelerated aging not typical for BS. RTS patients also show a high prevalence of cancers, especially...