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S M Berget

Publications and source records attributed to S M Berget.

60 records · Page 4Linked to original sources
PubMed1976

Adenovirus transcription. IV. Synthesis of viral-specific RNA in human cells infected with temperature-sensitive mutants of adenovirus 5.

Cytoplasmic RNA sequences produced in HeLa cells infected with the adeno-virus 5 temperature-sensitive mutants ts1, ts2, ts9, ts17, ts18, ts19, ts20, ts22, ts49, ts36, and ts125 were characterized by hybridization to DNA probes generated by strand separation of restriction endonuclease fragments of adenovirus 5 DNA. Two ""early'' mutants defective in DNA synthesis, ts125 and ts36, fail to make wild-type levels of all previously reported classes of late RNA at the nonpermissive temperature. At 40.5 degrees C, both ts125 and ts36 synthesize a wild-type complement of early cytoplasmic RNA 16 h after infection. Under these conditions, no ""late'' cytoplasmic RNA sequences were observed. Similarly, nuclear RNA present in these cells resembled early cytoplasmic RNA rather than late nuclear RNA. All the late adenovirus 5 temperature-sensitive mutants synthesized normal wild-type levels of late cytoplasmic RNA at the nonpermissive temperature, except ts2, which appears to overproduce certain cytoplasmic species.

Base Sequence↗
PubMed1975

Early events after infection of Escherichia coli by bacteriophage T5. Induction of a 5'-nucleotidase activity and excretion of free bases.

Thymine-containing compounds, produced degradation of Escherichia coli DNA after infection of the cells with bacteriophage T5, did not accumulate in the cell but were excreted into the medium as the DNA was degraded. The ultimate degradation product was extracellular thymine that was not reutilized when T5 DNA synthesis began. This excretion of thymine may have been due in part to the induction of 5'-nucleotidase activity within 3 min after T5 infection. The level of this activity reached a maximum between 4 to 6 min after infection and then rapidly declined to its preinfection level by 10 to 15 min after infection. Chloramphenicol added before or soon after infection prevented the appearance of the nucleotidase. The induced nucleotidase activity was active not only on dTMP but also on dAMP, dGMP, and dCMP.

Carbon Radioisotopes↗
PubMed1974

Isolation and partial characterization of bacteriophage T5 mutants deficient in the ability to induce deoxynucleoside monophosphate kinase.

Two mutants of bacteriophage T5 deficient in the ability to induce wild-type levels of deoxynucleoside monophosphate kinase were isolated and partially characterized. Both mutations were demonstrated to be in a structural gene for the kinase. One of the mutants, designated dnk 10, induces no detectable levels of dCMP, dGMP, or dTMP kinase activity. Because the mutant can successfully infect nonpermissive cells, phage-induced deoxynucleoside monophosphate kinase appears to be an unessential function for phage production. DNA synthesis in dnk 10-infected cells, however, is reduced to 30% of that observed in wild-type-infected cells; phage production is reduced by a comparable amount. The dnk mutation has been mapped and located on the "C" region of the T5 genetic map, 6.3 map units from the C1 locus.

Coliphages↗
PubMedDate not supplied

Are U4 small nuclear ribonucleoproteins involved in polyadenylation?

The mechanism whereby eukaryotic pre-messenger RNAs are polyadenylated is unknown. Most models for polyadenylation invoke cleavage of precursor transcripts at the site of poly(A) addition followed by polymerization of A residues by poly(A) polymerase. Analysis of the sequences surrounding poly(A) addition sites has identified the consensus recognition sequence element AAUAAA as necessary but not sufficient for polyadenylation. A second recognition sequence element CACUG , was observed by Benoit et al. to be adjacent to the site of poly(A) addition in several sequenced RNAs. Here, we analyse 61 vertebrate poly(A) addition sequences, define a more extensive recognition sequence for polyadenylation than previously recognized and suggest how the site of poly(A) addition may be chosen. Furthermore, we find that the defined recognition sequence has elements which are complementary to regions within the small nuclear RNA U4, suggesting that U4 small nuclear ribonucleoproteins (snRNPs) may mediate polyadenylation in a fashion similar to the role of U1 snRNPs in splicing. The model invokes hybridization of U4 RNA to AAUAAA recognition elements as related to primary site selection, and hybridization to CAYUG recognition elements as related to cleavage site selection.

Base Sequence↗