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T R Broker

Publications and source records attributed to T R Broker.

83 records · Page 5Linked to original sources
PubMed1977

An amazing sequence arrangement at the 5' ends of adenovirus 2 messenger RNA.

The 5' terminal sequences of several adenovirus 2 (Ad2) mRNAs, isolated late in infection, are complementary to sequences within the Ad2 genome which are remote from the DNA from which the main coding sequence of each mRNA is transcribed. This has been observed by forming RNA displacement loops (R loops) between Ad2 DNA and unfractionated polysomal RNA from infected cells. The 5' terminal sequences of mRNAs in R loops, variously located between positions 36 and 92, form complex secondary hybrids with single-stranded DNA from restriction endonuclease fragments containing sequences to the left of position 36 on the Ad2 genome. The structures visualized in the electron microscope show that short sequences coded at map positions 16.6, 19.6 and 26.6 on the R strand are joined to form a leader sequence of 150-200 nucleotides at the 5' end of many late mRNAs. A late mRNA which maps to the left of position 16.6 shows a different pattern of second site hybridization. It contains sequences from 4.9-6.0 linked directly to those from 9.6-10.9. These findings imply a new mechanism for the biosynthesis of Ad2 mRNA in mammalian cells.

Adenoviruses, Human↗
PubMed1975

A new method of in situ hybridization.

A new method for gene mapping at the chromosome level using in situ hybridization and scanning electron microscopy is described and has been applied to mapping the rRNA genes of Drosophila melanogaster. Biotin is covalently attached to Drosophila rRNA via a cytochrome c bridge at a ratio of one cytochrome-biotin per 130 nucleotides by a chemical procedure. Polymethacrylate spheres with a diameter of ca. 60 nm are prepared by emulsion polymerization and are covalently attached to the protein avidin at a ratio of 5-20 avidins per sphere. The biotin-labeled rRNA is hybridized to denatured DNA in a chromosome squash. Upon incubation with a sphere solution, some of the biotin sites become labeled with spheres because of the strong non-covalent interaction between biotin and avidin. The chromosome squash is examined in the scanning electron microscope (SEM). Polymer spheres, which are visible in the SEM, are observed to label the nucleolus, where the rRNA genes are located.

Animals↗
PubMed1975

Molecular and genetic recombination of bacteriophage T4.

Most genetic characteristics of T4 recombination (the effects of chromosomal termini on recombination, heterozygosity, high negative interference, base mismatch repair, polarized segregation, and the stimulation or depression of recombination in response to phage mutations or external perturbations) can be expressed adequately in terms of our present understanding of the molecular events of T4 infection cycles. T4 DNA replication begins and ends with linear chromosomes and does not require a circular intermediate. Replication is bi-directional, possibly from multiple origins. Two phases of replication are distinguishable: (a) an early mode during which about 20 progeny copies of infecting chromosomes are made prior to (b) a recombination-dependent mode during which progeny molecules associate to form covalently joined linear concatemers. Further replication is generally arrested if concatemerization is prevented. T4 DNA recombination depends on the production of single-stranded gaps and termini. If replication is inhibited, the single-stranded regions are produced by deoxyribonuclease activities. In contrast, during partial replication of damaged chromosomes, during slow replication when enzymes or subtrates are limited, and during normal replication, they are formed by strand-displacement DNA polymerization. As a rule, any agents or perturbations that cause an accumulation of single-stranded regions stimulate recombination, whereas efficient repair of such regions depresses it. Both the preservation and pairing of single-stranded regions are facilitated by the gene-32 single-stranded DNA binding protein. Covalent repair of strand interruptions between recombined DNA segments requires polymerases or nucleases as well as ligases.

Chromosome Mapping↗