In this task, you are given an abstract of article. Your task is to generate title for this article. Preferred titles are under thirty words.

Input: Consider Input: US28 is one of four 7 transmembrane (7TM) chemokine receptors encoded by human cytomegalovirus and has been shown to both signal and endocytose in a ligand-independent, constitutively active manner. Here we show that the constitutive activity and constitutive endocytosis properties of US28 are separable entities in this viral chemokine receptor. We generated chimeric and mutant US28 proteins that were altered in either their constitutive endocytic (US28 Delta 300, US28 Delta 317, US28-NK1-ctail, and US28-ORF74-ctail) or signaling properties (US28R129A). By using this series of mutants, we show that the cytoplasmic tail domain of US28 per se regulates receptor endocytosis, independent of the signaling ability of the core domain of US28. The constitutive endocytic property of the US28 c-tail was transposable to other 7TM receptors, the herpes virus 8-encoded ORF74 and the tachykinin NK1 receptor (ORF74-US28-ctail and NK1-US28-ctail). Deletion of the US28 C terminus resulted in reduced constitutive endocytosis and consequently enhanced signaling capacity of all receptors tested as assessed by inositol phosphate turnover, NF-kappa B, and cAMP-responsive element-binding protein transcription assays. We further show that the constitutive endocytic property of US28 affects the action of its chemokine ligand fractalkine/CX3CL1 and show that in the absence of the US28 C terminus, fractalkine/CX3CL1 acts as an agonist on US28. This demonstrates for the first time that the endocytic properties of a 7TM receptor can camouflage the agonist properties of a ligand.

Output: The carboxyl terminus of human cytomegalovirus-encoded 7 transmembrane receptor US28 camouflages agonism by mediating constitutive endocytosis.

Input: Consider Input: Glucagon is a 29-amino acid pancreatic hormone which counteracts the blood glucose-lowering action of insulin by stimulating hepatic glycogenolysis and gluconeogenesis1. The structure of the hamster pancreatic glucagon precursor has recently been determined from the sequence of a cloned cDNA2. Hamster preproglucagon is a 180-amino acid protein which contains five functional regions; a signal or pre-peptide, an NH2-terminal peptide (also called glicentin-related pancreatic peptide, GRPP), glucagon, and two carboxy-terminal glucagon-like peptides (GLP-1 and GLP-2). The sequences of two non-allelic anglerfish pancreatic glucagon precursors35 have also been determined and their organization is similar but not identical to the hamster protein; they lack the polypeptide segment corresponding to hamster GLP-2. The presence of three regions possessing internal homology, that is, glucagon, GLP-1 and GLP-2, within proglucagon, and the absence of GLP-2 in the anglerfish precursors suggests that the structure of the preproglucagon gene might provide insight into the evolution of this polyprotein. We have isolated and sequenced the human preproglucagon gene and report here that the organization of the human precursor deduced from this sequence is identical to the hamster protein. The gene contains at least three intervening sequences which divide the protein-coding portion of the gene into four regions corresponding to the signal peptide and part of the NH2-terminal peptide, the remainder of the NH2-terminal peptide and glucagon, GLP-1, and GLP-2. The data suggest that triplication and subsequent sequence divergence of an exon encoding glucagon or a glucagon-like peptide produced this polyprotein precursor.

Output: Exon duplication and divergence in the human preproglucagon gene

Input: Consider Input: Down syndrome (DS) children have a high frequency of acute megakaryoblastic leukemia (AMKL) in early childhood. At least 2 in utero genetic events are required, although not sufficient, for DS-AMKL: trisomy 21 (T21) and N-terminal-truncating GATA1 mutations. To investigate the role of T21 in DS-AMKL, we compared second trimester hemopoiesis in DS without GATA1 mutations to gestation-matched normal controls. In all DS fetal livers (FLs), but not marrows, megakaryocyte-erythroid progenitor frequency was increased (55.9% +/- 4% vs 17.1% +/- 3%, CD34(+)CD38(+) cells; P < .001) with common myeloid progenitors (19.6% +/- 2% vs 44.0% +/- 7%) and granulocyte-monocyte (GM) progenitors (15.8% +/- 4% vs 34.5% +/- 9%) commensurately reduced. Clonogenicity of DS-FL versus normal FL CD34(+) cells was markedly increased (78% +/- 7% vs 15% +/- 3%) affecting megakaryocyte-erythroid ( approximately 7-fold higher) and GM and colony-forming unit-granulocyte, erythrocyte macrophage, megakaryocyte (CFU-GEMM) progenitors. Replating efficiency of CFU-GEMM was also markedly increased. These data indicate that T21 itself profoundly disturbs FL hemopoiesis and they provide a testable hypothesis to explain the increased susceptibility to GATA1 mutations in DS-AMKL and DS-associated transient myeloproliferative disorder.
Output: Abnormalities in the myeloid progenitor compartment in Down syndrome fetal liver precede acquisition of GATA1 mutations.