Epilepsy, hyperalgesia, impaired memory, and loss of pre- and postsynaptic GABA(B) responses in mice lacking GABA(B(1)).

GABA(B) (gamma-aminobutyric acid type B) receptors are important for keeping neuronal excitability under control. Cloned GABA(B) receptors do not show the expected pharmacological diversity of native receptors and it is unknown whether they contribute to pre- as well as postsynaptic functions. Here, we demonstrate that Balb/c mice lacking the GABA(B(1)) subunit are viable, exhibit spontaneous seizures, hyperalgesia, hyperlocomotor activity, and memory impairment. Upon GABA(B) agonist application, null mutant mice show neither the typical muscle relaxation, hypothermia, or delta EEG waves. These behavioral findings are paralleled by a loss of all biochemical and electrophysiological GABA(B) responses in null mutant mice. This demonstrates that GABA(B(1)) is an essential component of pre- and postsynaptic GABA(B) receptors and casts doubt on the existence of proposed receptor subtypes.

A multifunctional exonuclease from vegetative Schizosaccharomyces pombe cells exhibiting in vitro strand exchange activity.

A 140-kDa polypeptide (p140) has been purified over 2000-fold from vegetative Schizosaccharomyces pombe cells using an assay of homologous pairing and strand exchange between linear double-stranded DNA (dsDNA) and circular single-stranded DNA (ssDNA) in vitro. Electron microscopic analysis of the reaction products showed displacement of one strand of the linear duplex DNA by the circular ssDNA molecule. In addition, the protein contained 5' to 3' exonuclease activity on ssDNA and dsDNA (with a 50-fold preference on the single-stranded substrate) as well as on single-stranded RNA. Furthermore, p140 was capable of renaturing complementary ssDNA as shown by S1 nuclease assays. p140 behaved like a monomer in solution under reaction conditions. Direct comparison of the biochemical properties, sequence analysis, and cross-reactivity to a monoclonal antibody suggests that p140 is probably identical with ExoII, purified from S. pombe meiotic cells as a ssDNA exonuclease (Szankasi, P., and Smith, G. R. (1992) Biochemistry 31, 6769-6773). Given the diverse activities of p140, the protein might be involved in DNA and/or RNA metabolism in vivo.

A specific DNA sequence is required for high frequency of recombination in the ade6 gene of fission yeast.

The point mutation M26 in the ade6 gene of Schizosaccharomyces pombe increases recombination frequency by an order of magnitude in comparison with other mutations in the same gene. The hypothesis is tested that this hot spot of recombination requires a specific nucleotide sequence at the M26 site. The DNA sequence is altered systematically by in vitro mutagenesis, and the resulting sequences are introduced into the ade6 gene in vivo by gene replacement. It results that any change of the heptanucleotide ATGACGT leads to loss of high frequency of recombination. Thus this oligonucleotide sequence is necessary for high frequency of recombination, but it seems not to be sufficient.