Large intragenic deletions of the NF2 gene: breakpoints and associated phenotypes.

In this study, the breakpoints of six large intragenic deletions in the NF2 gene are determined, which had initially been detected by multiplex ligation-dependent probe amplification. While one breakpoint occurred within an exon, the remaining 11 lied in the corresponding flanking introns. Two of the deletions were most likely caused by nonallelic homologous recombination between Alu sequences, while the other four appeared to be the result of nonhomologous endjoining, possibly facilitated by rearrangement-promoting elements at the junctions in some cases. The clinical features of patients with large intragenic deletions and individuals with mutations affecting single or multiple nucleotides of the NF2 gene are relatively similar. However, patients with deletions of the 3' exons 15 and 16 of the NF2 gene did exhibit milder phenotypes, especially with respect to the age of disease onset.

A novel member of the GCN5-related N-acetyltransferase superfamily from Caenorhabditis elegans preferentially catalyses the N-acetylation of thialysine [S-(2-aminoethyl)-L-cysteine].

The putative diamine N-acetyltransferase D2023.4 has been cloned from the model nematode Caenorhabditis elegans. The 483 bp open reading frame of the cDNA encodes a deduced polypeptide of 18.6 kDa. Accordingly, the recombinantly expressed His6-tagged protein forms an enzymically active homodimer with a molecular mass of approx. 44000 Da. The protein belongs to the GNAT (GCN5-related N-acetyltransferase) superfamily, and its amino acid sequence exhibits considerable similarity to mammalian spermidine/spermine-N1-acetyltransferases. However, neither the polyamines spermidine and spermine nor the diamines putrescine and cadaverine were efficiently acetylated by the protein. The smaller diamines diaminopropane and ethylenediamine, as well as L-lysine, represent better substrates, but, surprisingly, the enzyme most efficiently catalyses the N-acetylation of amino acids analogous with L-lysine. As determined by the k(cat)/K(m) values, the C. elegans N-acetyltransferase prefers thialysine [S-(2-aminoethyl)-L-cysteine], followed by O-(2-aminoethyl)-L-serine and S-(2-aminoethyl)-D,L-homocysteine. Reversed-phase HPLC and mass spectrometric analyses revealed that N-acetylation of L-lysine and L-thialysine occurs exclusively at the amino moiety of the side chain. Remarkably, heterologous expression of C. elegans N-acetyltransferase D2023.4 in Escherichia coli, which does not possess a homologous gene, results in a pronounced resistance against the anti-metabolite thialysine. Furthermore, C. elegans N-acetyltransferase D2023.4 exhibits the highest homology with a number of GNATs found in numerous genomes from bacteria to mammals that have not been biochemically characterized so far, suggesting a novel group of GNAT enzymes closely related to spermidine/spermine-N1-acetyltransferase, but with a distinct substrate specificity. Taken together, we propose to name the enzyme 'thialysine N(epsilon)-acetyltransferase'.

Extensive molecular genetic analysis of the 3p14.3 region in patients with Zimmermann-Laband syndrome.

Zimmermann-Laband syndrome (ZLS) is a rare autosomal dominant inherited disorder characterized by a coarse facial appearance, gingival fibromatosis, and absence or hypoplasia of the terminal phalanges and nails of hands and feet. Additional, more variable features include hyperextensibility of joints, hepatosplenomegaly, mild hirsutism, and mental retardation. Mapping of the translocation breakpoints of t(3;8) and t(3;17) found in patients with the typical clinical features of ZLS defined a common breakpoint region of approximately 280 kb located in 3p14.3, which includes the genes CACNA2D3 and WNT5A. Breakpoint cloning revealed that both translocations most likely occurred by non-homologous (illegitimate) recombination. Mutation analysis of nine genes located in 3p21.1-p14.3, including CACNA2D3, which is directly disrupted by one breakpoint of the t(3;17), identified no pathogenic mutation in eight sporadic patients with ZLS. Southern hybridization analysis and multiplex ligation-dependent probe amplification (MLPA) did not detect submicroscopic deletion or duplication in either CACNA2D3 or WNT5A in ZLS-affected individuals. Mutation analysis of nine conserved nongenic sequence elements (CNEs) in 3p21.1-p14.3, which were identified by interspecies comparison and may represent putative regulatory elements for spatiotemporally correct expression of nearby genes, did not show any sequence alteration associated with ZLS. Taken together, the lack of a specific coding-sequence lesion in the common region, defined by two translocation breakpoints, in sporadic patients with ZLS and an apparently normal karyotype suggests that either some other type of genetic defect in this vicinity or an alteration elsewhere in the genome could be responsible for ZLS.