Search PubMed⌕ Search

Biomedical subjects

O Laub

Publications and source records attributed to O Laub.

33 records · Page 2Linked to original sources
PubMed1980

5,6-dichloro-1-beta-ribofuranosylbenzimidazole enhances premature termination of late transcription of simian virus 40 DNA.

Short RNA chains initiating at the major promoter sites for simian virus 40 (SV40) late transcription are elongated to approximately 450 nucleotides in a molar ammount greater than that from any other region of the viral DNA. This conclusion is based on the following observations: (i) Transcriptional complexes isolated by Sarkosyl and by hypotonic leaching (minichromosomes) from nuclei of cells infected with SV40 as well as intact nuclei were pulse labeled in vitro with [alpha-32P]TUP and were observed to synthesize short RNA transcripts that hybridized predominantly to a SV40 DNA fragment spanning between 0.67 and 0.76 map units. (ii) In the presence of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a drug known to accentuate premature transcriptional termination, accumulation of these short SV40 RNA chains was enhanced. When SV40-infected cells were pretreated with DRB and then labeled in vivo or in vitro, they synthesized short labeled viral RNAs that hydridized almost exclusively with the DNA fragment spanning between 0.67 and 0.76 map units. These observations suggest a mechanism in the regulation of SV40 late transcription.

Animals↗
PubMed1979

Mechanism for circularization of linear DNAs: circular parvovirus MVM DNA is formed by a "noose" sliding in a "lasso"-like DNA structure.

During an electron-microscopic survey with the aim of identifying the parvovirus MVM transcription template, we observed previously unidentified structures of MVM DNA in lysates of virus-infected cells. These included double-stranded "lasso"-like structures and relaxed circles. Both structures were of unit length MVM DNA, indicating that they were not intermediates formed during replication; they each represented about 5% of the total nuclear MVM DNA. The proportion of these structures was unchanged after digestion with sodium dodecyl sulfate/Pronase and RNase and after mild denaturation treatment. Cleavage of the "lasso" structures with EcoRI restriction endonuclease indicated that the "noose" part of the "lasso" structure is located on the 5' side of the genomic single-stranded MVM DNA. A model is presented for the molecular nature of the circularization process of MVM DNA in which the "lasso" structures are identified as intermediates during circle formation. This model proposes a mechanism for circularization of linear DNAs.

DNA Replication↗
PubMed1978

Electron microscopic evidence for splicing of SV40 late mRNAs.

Poly(A)-containing SV40 cytoplasmic RNA was hybridized with linear double-stranded SV40 DNA and formed RNA displacement loops (R loops). The structures visualized in the electron microscope are consistent with the conclusion that the leader sequences at the 5' ends of the 16S and 19S late mRNAs are not coded immediately adjacent to the main portions of the mRNAs. These data are consistent with either segmentation of the leaders or heterogeneity of their lengths. Measurements carried out on the R loop structures have provided the locations, on the physical map of SV40 DNA, for the bodies and leaders of the 16S and 19S late mRNAs, and the lengths of the bodies, leaders and the corresponding intervening DNA sequences.

DNA, Viral↗
PubMed1978

The frequencies of transcription from the E- and L-strands of polyoma DNA.

Exhaustion type hybridization was used to measure the amount of nuclear virus RNA complementary to the early (E) and late (L) polyoma virus DNA strands. At 36 h after infection between 2.5 and 7.3% of the newly synthesized virus RNA was complementary to the E-strand (-strand) and between 92.7 and 97.5% was complementary to the L-strand (+strand). This proportion was independent of the labelling time, indicating similar accumulation of the E- and L-RNA transcripts in the nucleus. The nuclear E- and L-RNA transcripts sedimented in a similar manner through sucrose gradients.

Cell Line↗
PubMed1977

Novel mechanism for RNA maturation: the leader sequences of simian virus 40 mRNA are not transcribed adjacent to the coding sequences.

The 5'-terminal 100-200 ribonucleotides of late simian virus 40 (SV40) mRNAs are not transcribed immediately adjacent to their coding sequences. This conclusion is based on the following observations. The major late SV40 cytoplasmic RNA species, 16S and 19S, were purified from poly(A)-containing cytoplasmic RNA by hybridization to and elution from an SV40 DNA fragment that maps between 0.67 and 0.76. This fragment is remote from the DNA fragments that include the coding sequences. The RNA transcripts from the fragment located between 0.67 and 0.76 were found in abundance. Even though selected on oligo(dT)-cellulose columns, the 5'-terminal sequences did not contain poly(A) tails directly adjacent to their 3' termini. The 5' terminus of the 16S mRNA, as monitored by hybridization of the sequences adjacent to the "cap" structure, was found adjacent to the coding sequences when intact [3H]methyl-labeled RNA was hybridized with restriction fragments. However, after fragmentation, the methyl label of this same RNA hybridized with a fragment that is remote from the coding sequences and maps between 0.67 and 0.73. These results imply a novel mechanism for biosynthesis of SV40 mRNA.

DNA Restriction Enzymes↗
PubMed1975

Transcription of simian virus 40. V. Regulattion of simian virus 40 gene expression.

RNA "exhaustion type" hybridization was used to measure the complementarity of nuclear and cytoplasmic viral RNA to the early (E) and late (L) simian virus 40 (SV40) DNA strands. This type of hybridization measures the amount of labeled RNA complementary to each of the two DNA strands, rather than the fraction of each SV40 DNA strand that is homologous to SV40 RNA. At 48 h after infection, about 5% of the nuclear newly synthesized viral RNA was complementary to the E-strand (- strand) and 95% was complementary to the L-strand (+ strand). This proportion was independent of the labeling time, indicating similar accumulation of the E- and L-RNA transcripts in the nucleus. The nuclear E- and L-viral RNA transcripts sedimented in a similar manner on sucrose gradients. Of the cytoplasmic viral RNA only about 1% was complementary to the E-strand, these molecules sedimenting at 19S, whereas 99% were complementary to the L-strand and sedimented at 19S and 16S. The abundance of E-RNA transcripts in nuclei of cells infected with serially passaged virus was about four times higher than that in nuclei of cells infected with plaque-purified virus; however, the size and proportion of the corresponding cytoplasmic E- and L-RNA transcripts was independent of the type of virus used to infect the cells. According to these results at least two control mechanisms regulate viral gene expression in productively infected cells, one operates at the trnascriptional level and the second at the post-transcriptional level.

Cell Line↗