No abstract

). † These authors contributed equally to this work. SummaryScanning DNA sequences for mutations and polymorphisms has become one of the most challenging, often expensive and time-consuming obstacles in many molecular genetic applications, including reverse genetic and clinical diagnostic applications. Enzymatic mutation detection methods are based on the cleavage of heteroduplex DNA at the mismatch sites. These methods are often limited by the availability of a mismatchspecific endonuclease, their sensitivity in detecting one allele in a pool of DNA and their costs. Here, we present detailed biochemical analysis of five Arabidopsis putative mismatch-specific endonucleases. One of them, ENDO1, is presented as the first endonuclease that recognizes and cleaves all types of mismatches with high efficiency. We report on a very simple protocol for the expression and purification of ENDO1. The ENDO1 system could be exploited in a wide range of mutation diagnostic tools. In particular, we report the use of ENDO1 for discovery of point mutations in the gibberellin 3b-hydrolase gene of Pisum sativum. Twenty-one independent mutants were isolated, five of these were characterized and two new mutations affecting internodes length were identified. To further evaluate the quality of the mutant population we screened for mutations in four other genes and identified 5-21 new alleles per target. Based on the frequency of the obtained alleles we concluded that the pea population described here would be suitable for use in a large reverse-genetics project.

No abstract

␤-Arrestins have been implicated in regulating internalization of the parathyroid hormone receptor (PTHR), but the structural features in the receptor required for this effect are unknown. In the present study performed in HEK-293 cells, we demonstrated that different topological domains of PTHR are implicated in agonist-dependent receptor internalization; truncation of the cytoplasmic tail (PTHR-TR), selective mutations of the cytoplasmic tail to remove the sites of parathyroid hormone (PTH)-stimulated phosphorylation (PTHR-PD), and mutations in the third transmembrane helix (N289A) or in the third cytoplasmic loop (K382A) resulted in a 30 -60% reduction in 125 I-PTH-related protein internalization. To better define the role of these internalization determinants, we have tested the ability of these mutant PTHRs to associate with ␤-arrestins by using three different methodological approaches: 1) ability of overexpression of ␤-arrestins to restore the internalization of 125 I-PTH-related protein for the mutant PTHRs; 2) visualization of PTH-mediated trafficking of ␤-arrestin1 and -2 fused to the green fluorescent protein with receptors by confocal microscopy; 3) quantification of ␤-arrestin1-green fluorescent protein translocation by Western blot. Our data reveal that the receptor' cytoplasmic tail contains determinants of ␤-arrestin interaction that are distinct from the phosphorylation sites and are sufficient for transient association of ␤-arrestin2, but stable association requires receptor phosphorylation. Determinants in the receptor's core (Asn-289 and Lys-382) appear to regulate internalization of the receptor/␤-arrestin complex toward early endocytic endosomes during the initial step of endocytosis.Agonist binding to most G protein-coupled receptors (GPCRs) 1 is quickly followed by the internalization of the agonist-receptor complex into endocytic vesicles. The model developed from studies of the ␤ 2 -adrenergic receptor views internalization as a process facilitated by binding of ␤-arrestin proteins to agonist-activated receptors after phosphorylation of the receptors by G protein-coupled receptor kinases (GRKs) (1, 2). Phosphorylation of GPCRs by GRKs is a prerequisite for the mobilization of cytosolic ␤-arrestins. Binding of ␤-arrestins to GRK-phosphorylated receptors results in the physical uncoupling of receptors from their cognate G proteins and terminates agonist-mediated signaling (3, 4). It was shown recently that ␤-arrestins bind clathrin, a major component of the clathrinbased endocytic machinery, with high affinity and serve as an adaptor that targets activated and phosphorylated receptors to clathrin-coated pits (5-7). In the case of the ␤ 2 -adrenergic receptor, receptor internalization is the consequence of the formation of a complex between ␤-arrestin2, the clathrin adaptor protein AP2, clathrin, and the activated receptor (8). Internalization has at least two outcomes: directing the receptor to a compartment where the phosphates are removed, allowing resensitization, and movement of the r...