An excess of massive stars in the local 30 Doradus starburst.

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses ([Formula: see text]). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 [Formula: see text] and contains 32 ± 12% more stars above 30 [Formula: see text] than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 [Formula: see text], the IMF power-law exponent is [Formula: see text], shallower than the Salpeter value of 2.35.

The Bloom's syndrome gene product is homologous to RecQ helicases.

The Bloom's syndrome (BS) gene, BLM, plays an important role in the maintenance of genomic stability in somatic cells. A candidate for BLM was identified by direct selection of a cDNA derived from a 250 kb segment of the genome to which BLM had been assigned by somatic crossover point mapping. In this novel mapping method, cells were used from persons with BS that had undergone intragenic recombination within BLM. cDNA analysis of the candidate gene identified a 4437 bp cDNA that encodes a 1417 amino acid peptide with homology to the RecQ helicases, a subfamily of DExH box-containing DNA and RNA helicases. The presence of chain-terminating mutations in the candidate gene in persons with BS proved that it was BLM.

Somatic intragenic recombination within the mutated locus BLM can correct the high sister-chromatid exchange phenotype of Bloom syndrome cells.

Cells from persons with Bloom syndrome feature an elevated rate of sister-chromatid exchange (SCE). However, in some affected persons a minority of blood lymphocytes have a normal SCE rate. Persons who inherit the Bloom syndrome gene BLM identical by descent from a common ancestor very rarely exhibit this high-SCE/low-SCE mosaicism; conversely, mosaicism arises predominantly in persons who do not share a common ancestor. These population data suggested that most persons with Bloom syndrome in whom the exceptional low-SCE cells arise are not homozygous for a mutation at BLM but instead are compound heterozygotes. Following this clue, we carried out a genotype analysis of loci syntenic with BLM in 11 persons who exhibited mosaicism. In five of them, polymorphic loci distal to BLM that were heterozygous in their high-SCE cells had become homozygous in their low-SCE cells, whereas heterozygous loci proximal to BLM remained heterozygous. These observations are interpreted to mean that intragenic recombination between paternally derived and maternally derived mutated sites within BLM can generate a functionally wild-type gene and that low-SCE lymphocytes are progeny of a somatic cell in which such intragenic recombination had occurred.

Cloning, sequence analysis and expression of two forms of mRNA coding for the human beta 2 subunit of the GABAA receptor.

Two forms of cDNA coding for the human GABAA beta 2 subunit have been cloned and sequenced. The two sequences differ by a 114 base pair insertion. The insert contains a phosphorylation consensus sequence for calmodulin-dependent protein kinase II. Quantitative PCR studies show that h beta 2L cDNA represents 10-15% of total h beta 2 cDNA in the 10 brain substructures tested. Analysis of human genomic southern blots suggests that the two forms might arise by differential splicing.

Stable expression of cloned rat GABAA receptor subunits in a human kidney cell line.

A predominant form of the GABAA/benzodiazepine receptor-Cl- channel complex is believed to consist of three different 48-55 kDa subunits (alpha, beta, gamma) with unknown stoichiometry. Plasmids containing the rat GABAA receptor cDNAs coding for alpha 1, beta 2, and gamma 2 were co-transfected, along with a plasmid encoding G418 resistance, into human embryonic kidney cells previously transformed with Adenovirus 5 (HEK-293) [J. Gen. Virol., 36 (1977) 59-72]. Four percent of the G418 resistant colonies were found to express mRNA for all three of the GABAA subunits constitutively. A single cell clone derived from one of the alpha 1 beta 2 gamma 2 expressors has demonstrated stable electrophysiological characteristics over 25 passages. The GABA-activated Cl- current in this cell line is blocked by picrotoxin and bicuculline, and is modulated by a variety of agonist and inverse agonist ligands including diazepam, Ro 154513, zolpidem, and beta-CCE. The cell line has been used successfully over a 12-month period as a screen for novel drugs modulating GABA-mediated polarization of neuronal cells.

Functional expression of GABAA chloride channels and benzodiazepine binding sites in baculovirus infected insect cells.

We have employed the baculovirus expression system for the production of insect cell membranes having GABA/benzodiazepine binding sites. Three recombinant baculoviruses each harboring a different GABAA receptor cDNA were introduced into insect cells by simultaneous infection. Infected cells expressed GABA responsive Cl- channels and benzodiazepine binding sites with the same pharmacological specificity as animal cells expressing these receptor subunits.