Molecular Cloning and Physical Mapping of the Daptomycin Gene Cluster from Streptomyces roseosporus

The daptomycin biosynthetic gene cluster of Streptomyces roseosporus was analyzed by Tn5099 mutagenesis, molecular cloning, partial DNA sequencing, and insertional mutagenesis with cloned segments of DNA. The daptomycin biosynthetic gene cluster spans at least 50 kb and is located about 400 to 500 kb from one end of the ~7,100-kb linear chromosome. We identified two peptide synthetase coding regions interrupted by a 10- to 20-kb region that may encode other functions in lipopeptide biosynthesis.     

Multiple products of the Drosophila Shaker gene may contribute to potassium channel diversity

K+ channels are known through electrophysiology and pharmacology to be an exceptionally diverse group of channels. Molecular studies of the Shaker (Sh) locus in Drosophila have provided the first glimpse of K+ channel structure. The sequences of several Sh cDNA clones have been reported; none are identical. We have isolated and examined 18 additional Sh cDNAs in an attempt to understand the origin, extent, and significance of the variability. The diversity is extensive: we have already identified cDNAs representing at least nine distinct types, and Sh could potentially encode 24 or more products. This diversity, however, fits a simple pattern in which variable 3' and 5' ends are spliced onto a central constant region to yield different cDNA types. These different Sh cDNAs encode proteins with distinct structural features.     

Genetic Analysis of the Shaker Gene Complex of Drosophila Melanogaster

The Shaker complex (ShC) spans over 350 kb in the 16F region of the X chromosome. It can be dissected by means of aneuploids into three main sections: the maternal effect (ME), the viable (V) and the haplolethal (HL) regions. The mutational analysis of ShC shows a high density of antimorphic mutations among 12 lethal complementation groups in addition to 14 viable alleles. The complex is the structural locus of a family of potassium channels as well as a number of functions relevant to the biology of the nervous system. The constituents of ShC seem to be linked by functional relationships in view of the similarity of the phenotypes, antimorphic nature of their mutations and the behavior in transheterozygotes. We discuss the relationship between the genetic organization of ShC and the functional coupling of potassium currents with the other functions encoded in the complex.     

Shaker K+ channel subunits from heteromultimeric channels with novel functional properties.

A large number of related genes (the Sh gene family) encode potassium channel subunits which form voltage-dependent K+ channels by aggregating into homomulitimers. One of these genes, the Shaker gene in Drosophila, generates several products by alternative splicing. These products encode proteins with a constant central region flanked by variable amino and carboxyl domains. Coinjection of two Shaker RNAs with different amino or different carboxyl ends into Xenopus oocytes produces K+ currents that display functional properties distinct from those observed when each RNA is injected separately, indicating the formation of heteromultimeric channels. The analysis of Shaker heteromultimers suggests certain rules regarding the roles of variable amino and carboxyl domains in determining kinetic properties of heteromultimeric channels. Heteromultimers with different amino ends produce currents in which the amino end that produces more inactivation dominates the kinetics. In contrast, heteromultimers with different carboxyl ends recover from inactivation at a rate closer to that observed in homomultimers of the subunit which results in faster recovery. While this and other recent reports demonstrate that closely related Sh family proteins form functional heteromultimers, we show here that two less closely related Sh proteins do not seem to form functional heteromultimeric channels. The data suggest that sites for subunit recognition may be found in sequences within a core region, starting about 130 residues before the first membrane spanning domain of Shaker and ending after the last membrane spanning domain, which are not conserved between Sh Class I and Class III genes.     

Analysis of genes for 5S rRNA from the cricket, Acheta domesticus: two classes of repeating units

To examine the modulation of 5S rRNA gene activity during development in the cricket, Acheta domesticus, 5S X DNA was isolated from a lambda Charon 4 genomic library and characterized. Southern blot analysis of cloned A. domesticus genomic DNA revealed that restriction fragments of 3.0 and 2.1 kb represent two size classes of 5S X DNA repeating units; over 90% of the repeats measure 3.0 kb. Restriction analysis of two 5S X DNA clones suggests that the 2.1-kb repeats are not randomly interspersed within clusters of the larger 3.0-kb repeating units. Heteroduplex and restriction mapping of several clones indicate that the spacers of both repeating units account for their unusual length. The major difference between the two classes of repeats may lie in 0.9-kb spacer sequences to the 3.0-kb repeats.     

Essential structure in the cloned transforming DNA that induces gene amplification of the Bacillus subtilis amyE-tmrB region.

Bacillus subtilis B7, a mutant which acquired gene amplification of the amyE-tmrB region, showed, as a result, hyperproductivity (about a 5- to 10-fold increase) of alpha-amylase and tunicamycin resistance. The mutational character was transferred to recipient cells by competence transformation. A 14-kilobase (kb) EcoRI chromosomal DNA fragment of strain B7 was found to have the transforming activity. We cloned a 6.4-kb EcoRI fragment on a phage vector lambda Charon 4A through a spontaneous deletion of 7.6 kb from the 14-kb fragment and subcloned a 1.6-kb HindIII fragment on pGR71. The cloned 6.4-kb EcoRI and 1.6-kb HindIII fragments retained the transforming activity of inducing gene amplification of the amyE-tmrB region. At the junction point (J) of the repeating units (16 kb), the tmrB gene was linked to a DNA region (M) located 4 kb upstream of amyE. The essential structure of the cloned, transforming (gene amplification-inducing) DNA was deduced to be that around J. The subcloned 1.6-kb HindIII fragment that retained the transforming activity was shown to be almost solely composed of the tmrB-J-M region. In addition, the DNA sequence around J was determined.     

Structure of the FBJ murine osteosarcoma virus genome: molecular cloning of its associated helper virus and the cellular homolog of the v-fos gene from mouse and human cells.

The 8.2-kilobase (kb) unintegrated circular DNA form of the FBJ murine leukemia virus (FBJ-MLV) was linearized by cleavage at the single HindIII site, molecularly cloned into bacteriophage Charon 30, and subsequently subcloned into pBR322 (pFBJ-MLV-1). Both FBJ-MLV virion RNA and pFBJ-MLV-1 DNA were used to investigate the arrangement of helper virus sequences in the FBJ murine osteosarcoma virus genome (FBJ-MSV) by heteroduplex formation with cloned FBJ-MSV proviral DNA. The results showed that the FBJ-MSV genome contained 0.8 kb of helper virus sequence at its 5' terminus and 0.98 kb at its 3' terminus. Approximately 6.8 kb of helper virus sequence had been deleted, and 1.7 kb of unrelated sequence was inserted into the FBJ-MSV genome. This substituted region contains v-fos, the transforming gene of FBJ-MSV. Using a probe specific for v-fos, we have cloned homologous sequences (c-fos) from mouse and human chromosomal DNA. Heteroduplex analysis of FBJ-MSV DNA with these recombinant clones showed that both the c-fos(mouse) and the c-fos(human) sequences hybridized to the entire 1.7-kb v-fos region. However, five regions of homology of 0.27, 0.26, 0.14, 0.5, and 0.5 kb were separated by four regions of nonhomology of 0.76, 0.55, 0.1, and 0.1 kb from 5' to 3' with respect to the FBJ-MSV genome. The size of these sequences showed striking similarity in both c-fos(mouse) and c-fos(human).