[Physical map of the DNA of bacteriophage phiB]

A physical map of DNA phi B bacteriophage was constructed. Using the data of denaturation maps and heteroduplex analysis the positions of 10 (from 11) peaks were estimated. These peaks belong to DNA regions obtained after hydrolysis of phi B DNA by EcoRI endonuclease. This map is orientated to the end of the DNA molecule, which first entered the head, during phage maturation. The disposition of AT-enriched regions of the DNA molecule were shown.

Properties of erythromycin-inducible transposon Tn917 in Streptococcus faecalis

Streptococcus faecalis strain DS16 harbors two plasmids, a conjugative plasmid, pAD1, which encodes hemolysin and bacteriocin activities, and a nonconjugative plasmid, pAD2, encoding resistance to streptomycin, kanamycin, and erythromycin, the latter of which is inducible. The erythromycin resistance determinant is located on a 3.3-megadalton transposable element designated Tn917, which could be transposed to pAD1 as well as to two other plasmids, pAm gamma 1 and pAM alpha 1. When strain DS16 was exposed to low (inducing) concentrations of erythromycin for a few hours, the frequency of Tn917 transposition from pAD2 to pAD1 increased by an order of magnitude. This induction paralleled induction of erythromycin resistance and was prevented by exposing the cells to inhibitors of deoxyribonucleic acid, ribonucleic acid or protein synthesis. The exposure of strain DS16 to inducing concentrations of erythromycin also enhanced the frequency of erythromycin-resistant transconjugants appearing during mating. Initially, cointegrate molecules, whose molecular weights were approximately the sum of pAD1 and pAD2, accounted for these transconjugants; however, as the induction time increased, pAD1::Tn917 became increasingly prominent.

The presence of RNA in a double helix inhibits its interaction with histone protein

The binding of core histones (H2A, H2B, H3, H4) to a circular plasmid DNA and to a circular DNA-RNA hybrid molecule of similar size has been compared. Circular hybrid molecules were formed from single stranded fd DNA by synthesis of the complimentary strand with ribonucleotides using wheat germ RNA polymerase II. Upon reconstitution of plasmid DNA circles with histone, the sedimentation profiles of the DNA remained sharp by increased several fold in rate. Material from the peak fractions of these sedimentations appeared to be condensed circular loops of nucleosomes when examined by electron microscopy (EM), and the mass ratio of DNA to histone (at the histone concentrations which produced the fastest sedimentations) was typical of native chromatin. In contrast, the sedimentation behavior of DNA-RNA hybrid circles after addition of histone remained unchanged except for a minor fraction which exhibited a broad and faster sedimentation rate. Examination by EM revealed that most of the molecules appeared identical to protein free hybrid circles while the minor, faster sedimenting fraction appeared to be two or more circles bound together by protein aggregates. Finally, a linear molecule consisting of about 3000 base pairs of duplex DNA covalently joined on both ends to 1500 base pairs of RNA-DNA hybrid helix was constructed. Reconstitution of this molecule with core histone showed nucleosome formation only on the central DNA duplex region. Isopycnic banding of fixed hybrid-histone mixtures showed that little or no histone had bound to the bulk of the full hybrid molecules. We suggest that the presence of RNA in a nucleic acid duplex inhibits the condensation of the duplex into a nucleosomal structure by histone.

A DNA segment from D. melanogaster which contains five tandemly repeating units homologous to the major rDNA insertion

We describe a cloned segment of D. melanogaster DNA (cDm219) that contains five tandemly arranged sequence units homologous to the type I insertion sequence found in the majority of 28S rRNA genes on the X chromosome. Heteroduplex studies show that two of the units have a deletion corresponding to a 1.1 kb piece of DNA close to the right-hand end of the type I insertion. Another unit has a 7.5 kb sequence (zeta) substituted for a 0.95 kb piece of DNA close to the left-hand part of the type I rDNA insertion. The two remaining units are interrupted by the Col E1 plasmid vector. There are also differences in the restriction endonuclease cleavage maps both between the units of cDm219 themselves and compared to the restriction endonuclease cleavage maps of cloned rDNA segments that contain type I insertions. Quantitation of the gel transfer hybridization of zeta element probes to restriction endonuclease digests of D. melanogaster DNA indicates there are 30--40 copies of zeta sequences distributed in seven major arrangements within the haploid genome. The hybridization of zeta and insertion sequence probes to a library of D. melanogaster DNA segments cloned in bacteriophage lambda indicates at least 4--6 copies of the zeta element could be linked to insertion sequences. The common site of in situ hybridization of zeta sequences is to the chromocentral heterochromatin of polytene chromosomes.

[Molecular structure of hybrid phage phi80hy43]

The phage hybrid phi80hy43 derived from a vegetative cross phi80cIhlambda x lambdacIc17 was constructed for discrimination phi80mono- and polylysogens. Molecular structure of this hybrid was established using heteroduplex analysis and restriction endonuclease EcoRI. It is found that the hybrid phi80hy43 represents a phage phi80 containing a foreign piece of DNA between genes cI and 0. The length of this piece of DNA comprises 0.7%, corresponding to the length of cy-cII region of th phage lambda. So it is believed that the hybrid phi80hy43 was formed due to insertion of the lambdacy region with the mutation c17 into phi80hlambda phage genome.

Bleomycin fragmentation of duplex DNA occurs as staggered single-strand scissions

Electron microscopy of purified full-length linear duplex molecules produced by bleomycin reaction with PM2 DNA revealed low frequencies of closed circular duplex molecules as well as linear duplex molecules with opposed ends (cyclized molecules which have dissociated to yield a gap between the termini). The occurrence of these latter forms indicates that double-strand scissions produced by bleomycin reaction consist of two single-strand scissions which are physically staggered on the complementary strands. Analysis of the temperature dependence for cyclization led to the estimate that an average of 1.7 +/- 0.44 base-pairs (2.6 +/- 0.5 base pairs without base-stacking energies) occur between the staggered breaks. The reassociated termini cannot be ligated with T4 ligase. When PM2 DNA was fragmented at several sites within each molecule, circular duplexes and linear duplexes with opposed ends with a range of sizes from 350 base pairs up to full-length PM2 DNA were observed. Analysis of the frequency distribution of lengths of these fragments indicates that most, if not all, of the specific sites for bleomycin-directed double-strand scissions in PM2 DNA contain representatives of the same two base single-stranded termini.

Pilus-specific, lipid-containing bacteriophages PR4 and PR772: comparison of physical characteristics of genomes

The genomes of pilus-specific, lipid-containing phages PR4 and PR772 were studied electron microscopically. An identical mol. wt. of 10.9 x 10(6) was obtained. The genomes are unique (non-permuted) and have cohesive ends. From the similarities in size and denaturation maps of the genomes and failue to demonstrate non-homology in heteroduplexes, reported morphological ambiguities were clarified. The known serological difference between the phages could not be related to non-homology of their genomes. It is concluded that phages PR4 and PR772 are the same phage.

Genome complexities of the three mRNA species of snowshoe hare bunyavirus and in vitro translation of S mRNA to viral N polypeptide

The genome complexities of the principal intracellular viral complementary RNA species of the snowshoe hare bunyavirus have been analyzed by duplex analyses involving hybridization of complementary RNA to individual 32P-labeled viral RNA species (large, L; medium, M; and small, S), recovery of nuclease-resistant duplexes, and determination of the oligonucleotide fingerprints of the protected 32P-labeled viral sequences. The result for the M RNA (which codes for the glycoproteins G1 and G2; J. R. Gentsch and D. H. L. Bishop, J. Virol. 30:767-770, 1979) indicates that there is a single polycistronic M mRNA. Similar results were obtained for the L and S RNA species. In vitro translation studies with the S complementary RNA species of snowshoe hare virus as well as melted purified S duplexes substantiate earlier genetic and molecular studies (J. R. Gentsch and D. H. L. Bishop, J. Virol. 28:417-419, 1978; J. Gentsch, D. H. L. Bishop, and J. F. Obijeski, J. Gen. Virol. 34-257-268, 1977), which indicate that S mRNA codes for the virion nucleocapsid protein N.

Taxonomy of Clostridium tetani and related species

Clostridium tetani and its related species C. tetanomorphum, C. cochlearium and C. lentoputrescens were examined for DNA-DNA homology and biochemical properties. Two distinctly different groups were included under the name of C. tetanomorphum: one was identical with C. cochlearium and the name C. tetanomorphum was applied to the other group with some amendment of biochemical properties. Comparison of the type strain of C. lentoputrescens with wild strains obtained from horse faeces indicated that the name C. lentoputrescens should be abolished as a later synonym of C. cochlearium. Liquefaction of gelatin and spore shape, which have been used as the important criteria for differentiation of C. tetani-related species, were genetically insignificant.