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<jats:p> A lymphocyte population that expresses surface markers found on T cells and natural killer (NK) cells secretes large amounts of interleukin-4 (IL-4) immediately after T cell receptor ligation. These NK-like T cells are thus thought to be important for the initiation of type 2 T helper cell (T <jats:sub>H</jats:sub> 2) responses. CD1-deficient mice were found to lack this lymphocyte subset, but they could nevertheless mount a protypical T <jats:sub>H</jats:sub> 2 response; after immunization with antibody to immunoglobulin D (IgD), CD1-deficient mice produced IgE. Thus, although dependent on CD1 for their development, IL-4-secreting NK-like T cells are not required for T <jats:sub>H</jats:sub> 2 responses. </jats:p>

<jats:p> Mutations in the <jats:italic>Caenorhabditis elegans</jats:italic> gene <jats:italic>clk-1</jats:italic> affect biological timing and extend longevity. The gene <jats:italic>clk-1</jats:italic> was identified, and the cloned gene complemented the <jats:italic>clk-1</jats:italic> phenotypes and restored normal longevity. The CLK-1 protein was found to be conserved among eukaryotes, including humans, and structurally similar to the yeast metabolic regulator Cat5p (also called Coq7p). These proteins contain a tandem duplication of a core 82-residue domain. <jats:italic>clk-1</jats:italic> complemented the phenotype of <jats:italic>cat5/coq7</jats:italic> null mutants, demonstrating that <jats:italic>clk-1</jats:italic> and <jats:italic>CAT5/COQ7</jats:italic> share biochemical function and that <jats:italic>clk-1</jats:italic> acts at the level of cellular physiology. </jats:p>

<jats:p> Heterodimerization between members of the Bcl-2 family of proteins is a key event in the regulation of programmed cell death. The molecular basis for heterodimer formation was investigated by determination of the solution structure of a complex between the survival protein Bcl-x <jats:sub>L</jats:sub> and the death-promoting region of the Bcl-2-related protein Bak. The structure and binding affinities of mutant Bak peptides indicate that the Bak peptide adopts an amphipathic α helix that interacts with Bcl-x <jats:sub>L</jats:sub> through hydrophobic and electrostatic interactions. Mutations in full-length Bak that disrupt either type of interaction inhibit the ability of Bak to heterodimerize with Bcl-x <jats:sub>L</jats:sub> . </jats:p>

<jats:p> In the yeast <jats:italic>Saccharomyces cerevisiae</jats:italic> , telomere elongation is negatively regulated by the telomere repeat-binding protein Rap1p, such that a narrow length distribution of telomere repeat tracts is observed. This length regulation was shown to function independently of the orientation of the telomere repeats. The number of repeats at an individual telomere was reduced when hybrid proteins containing the Rap1p carboxyl terminus were targeted there by a heterologous DNA-binding domain. The extent of this telomere tract shortening was proportional to the number of targeted molecules, consistent with a feedback mechanism of telomere length regulation that can discriminate the precise number of Rap1p molecules bound to the chromosome end. </jats:p>

<jats:p>In normal human cells, damage due to ultraviolet light is preferentially removed from active genes by nucleotide excision repair (NER) in a transcription-coupled repair (TCR) process that requires the gene products defective in Cockayne syndrome (CS). Oxidative damage, including thymine glycols, is shown to be removed by TCR in cells from normal individuals and from xeroderma pigmentosum (XP)-A, XP-F, and XP-G patients who have NER defects but not from XP-G patients who have severe CS. Thus, TCR of oxidative damage requires an XPG function distinct from its NER endonuclease activity. These results raise the possibility that defective TCR of oxidative damage contributes to the developmental defects associated with CS.</jats:p>

<jats:p> Once a specific number of cells have been produced in the early <jats:italic>Xenopus laevis</jats:italic> embryo, replicon size during the S phase of the cell cycle increases. Here, it is reported that similar increase in replicon size occurred when the concentration of nuclei in replication-competent <jats:italic>Xenopus</jats:italic> egg extracts exceeded a critical threshold. In this system, the origin recognition complex (ORC) did not become stoichiometrically limiting for initiation, and similar amounts of this complex bound to chromatin regardless of replicon size. These data suggest that in early development, an unidentified factor controls how many preformed ORC-DNA complexes initiate DNA replication. </jats:p>