Genomic Organization of the Human Skeletal Muscle Sodium Channel Gene

Voltage-dependent sodium channels are essential for normal membrane excitability and contractility in adult skeletal muscle. The gene encoding the principal sodium channel α-subunit isoform in human skeletal muscle (SCN4A) has recently been shown to harbor point mutations in certain hereditary forms of periodic paralysis. We have carried out an analysis of the detailed structure of this gene including delineation of intron-exon boundaries by genomic DNA cloning and sequence analysis. The complete coding region of SCN4A is found in 32.5 kb of genomic DNA and consists of 24 exons (54 to > 2.2 kb) and 23 introns (97 bp-4.85 kb). The exon organization of the gene shows no relationship to the predicted functional domains of the channel protein and splice junctions interrupt many of the transmembrane segments. The genomic organization of sodium channels may have been partially conserved during evolution as evidenced by the observation that 10 of the 24 splice junctions in SCN4A are positioned in homologous locations in a putative sodium channel gene in Drosophila (para). The information presented here should be extremely useful both for further identifying sodium channel mutations and for gaining a better understanding of sodium channel evolution.     

A Genetic and Mosaic Analysis of a Locus Involved in the Anesthesia Response of Drosophila Melanogaster

We describe a genetic and behavioral analysis of several alleles of har38, a mutant with altered sensitivity to the general anesthetic halothane. We obtained a P-element-induced allele of har38 and generated several excision alleles by remobilizing the P element. The mutants narrow abdomen (na) and har85 are confirmed to be allelic to har38. Besides a decreased sensitivity to halothane, all mutant alleles of this locus cause a characteristic walking behavior in the absence of anesthetics. We have quantified this behavior using a geotaxis apparatus. Responses of the mutant alleles to different inhalational anesthetics were tested. The results strongly favor a multipathway model for the onset of anesthesia. Mosaic flies were tested for their response to halothane and checked for their abnormal walking behavior. The analysis suggests that both the behaviors are exhibited only by such mosaics as have the entire head of mutant origin. It is likely that this focus represents an element of a common pathway in the anesthetic response to several inhalational anesthetics but not all. This result is the first demonstration of regional specificity in the CNS of any animal for general anesthetic action.     

Activation mechanism of tris(2,3-dibromopropyl)phosphate to the potent mutagen, 2-bromoacrolein

The potent mutagen 2- bromoacrolein is formed from the carcinogenic flame retardant tris(2,3-dibromopropyl)phosphate (Tris-BP) on incubation with hepatic microsomes. Substitution of deuterium for hydrogen at the terminal carbon atoms (C-3) of Tris-BP significantly decreased both the mutagenic response and the formation rate of 2- bromoacrolein . Mass spectral analysis of the 2- bromoacrolein that was formed from the selectively deuterated analogs of Tris-BP revealed that the primary mechanism for the formation of 2- bromoacrolein involves an initial oxidative dehalogenation at C-3 followed by a beta-elimination reaction.     

A portable DNA sequence carrying the cohesive site (cos) of bacteriophage lambda and the mob (mobilization) region of the broad-host-range plasmid RK2: a module for the construction of new cosmids

A polylinker DNA sequence carrying the cos site of bacteriophage lambda and the mob (oriT) region of the IncP group plasmid RK2 was constructed. This composite polylinker has EcoRI sites at both termini and also unique sites for ClaI, HindIII, PstI and XbaI. The cos-mob region is portable with the use of EcoRI or a combination of EcoRI with ClaI, HindIII or XbaI. Another cos-mob cassette was also constructed from which the cos-mob region can be lifted with HindIII, ClaI or either of these enzymes in combination with others. These cos-mob cassettes can be used in constructing new cosmids that can be mobilized into a variety of Gram-negative bacteria. Using one of these cassettes we have constructed a small IncW group cosmid (11.1 kb) that was mobilizable into Escherichia coli, Rhizobium spp. and Alcaligenes eutrophus at high frequency.     

Oxidant effect of acetylphenylhydrazine: a comparative study with erythrocytes of several animal species.

Red cells from several animal species were treated with acetylphenylhydrazine and a comparative study of the oxidation of hemoglobin (Hb) and glutathione (GSH) made. Wide interspecies differences were observed but the oxidation of GSH paralleled that of Hb. Added glucose protected both Hb and GSH from oxidation; GSH by itself exercises a protective effect on Hb. The characteristic rates of oxidation of GSH in the different species can be observed only in the presence of oxyhemoglobin but not carboxyhemoblobin or methemoglobin. The oxidation of Hb appears to be the primary event, the oxidation of GSH being a consequence thereof.     

Sequence homology between Inc N group plasmids

DNA-DNA hybridization combined with "Southern blotting" was used to analyse the genetic organization and the nucleotide sequence homology between different regions of a previously characterized Inc N group plasmid pCUI and nine other Inc N group plasmids. The following conclusions could be reached: (1) N plasmids isolated from different parts of the world share substantial DNA sequence homology and also some similarity of overall genetic organization, (2) the majority of the N plasmids used in this study showed conservation of distribution of BglII and KpnI cleavage sites. Often, restriction endonuclease fragments of similar electrophoretic mobility encoded the same genetic function, (3) in one case, the N-specific properties appear to be integrated into the bacterial chromosome. (4) the plasmid DNA in strains carrying two Inc N plasmids, R199 and R113 were each composed of two molecular species only one of which constituted an N group plasmid.     

Sequence-specific 1H NMR assignments and secondary structure in solution of Escherichia coli trp repressor

Sequence-specific 1H NMR assignments are reported for the active L-tryptophan-bound form of Escherichia coli trp repressor. The repressor is a symmetric dimer of 107 residues per monomer; thus at 25 kDa, this is the largest protein for which such detailed sequence-specific assignments have been made. At this molecular mass the broad line widths of the NMR resonances preclude the use of assignment methods based on 1H-1H scalar coupling. Our assignment strategy centers on two-dimensional nuclear Overhauser spectroscopy (NOESY) of a series of selectively deuterated repressor analogues. A new methodology was developed for analysis of the spectra on the basis of the effects of selective deuteration on cross-peak intensities in the NOESY spectra. A total of 90% of the backbone amide protons have been assigned, and 70% of the alpha and side-chain proton resonances are assigned. The local secondary structure was calculated from sequential and medium-range backbone NOEs with the double-iterated Kalman filter method [Altman, R. B., & Jardetzky, O. (1989) Methods Enzymol. 177, 218-246]. The secondary structure agrees with that of the crystal structure [Schevitz, R., Otwinowski, Z., Joachimiak, A., Lawson, C. L., & Sigler, P. B. (1985) Nature 317, 782], except that the solution state is somewhat more disordered in the DNA binding region and in the N-terminal region of the first alpha-helix. Since the repressor is a symmetric dimer, long-range intersubunit NOEs were distinguished from intrasubunit interactions by formation of heterodimers between two appropriate selectively deuterated proteins and comparison of the resulting NOESY spectrum with that of each selectively deuterated homodimer. Thus, from spectra of three heterodimers, long-range NOEs between eight pairs of residues were identified as intersubunit NOEs, and two additional long-range intrasubunits NOEs were assigned.     

Condensation of chromatin into chromosomes preserves an open configuration but alters the DNase I hypersensitive cleavage sites of the transcribed gene

DNase I was used to probe the molecular organization of the chicken ovalbumin (OV) gene and glyceraldehyde 3-phosphate dehydrogenase (GPD) gene in interphase nuclei and in metaphase chromosomes of cultured chicken lymphoblastoid cells (MSB-1 line). The OV gene was not transcribed in this cell line, whereas the GPD gene was constitutively expressed. The GPD gene was more sensitive to DNase I digestion than the OV gene in both interphase nuclei and metaphase chromosomes, as determined by Southern blotting and liquid hybridization techniques. In addition, we observed DNase I hypersensitive sites around the 5' region of the GPD gene. These hypersensitive sites were not always at the same locations between the interphase nuclei and metaphase chromosomes. Our results suggest that chromatin condensation and decondensation during cell cycle alters nuclease hypersensitive cleavage sites.