Preferential binding of E. coli RNA polymerase to the AT-rich regions of bacteriophage f1 DNA

Mechanism of poly(A) synthesis by vaccinia virus

Data are presented which indicate that vaccinia DNA does not contain poly(dT) sequences the size of poly(A) sequences (50 to 200 nucleotides in length) found in vaccinia RNA. A hybridization experiment and polyacrylamide gel electrophoresis and DEAE-Sephadex chromatography of pyrimidine tracts show that poly(dT) sequences can account for no more than 0.1% of vaccinia DNA. Ultraviolet irradiation (which causes thymine dimer formation) and phleomycin (which binds to thymidine) both inhibit RNA synthesis but not poly(A) synthesis by vaccinia cores. These data are consistent with a nontranscriptive mechanism for vaccinia poly(A) synthesis. Both trypsin and 50 C heat treatment inhibit RNA synthesis more than poly(A) synthesis by cores, suggesting that separate enzymes may be involved in these syntheses. When the rate of core RNA synthesis is reduced by lowering the UTP and GTP concentrations, the size of the poly(A) sequences increase. These and other data suggest that transcription is involved in the termination of poly(A) synthesis in cores. This might be due to the displacement of growing poly(A) chains by recently completed RNA 3' termini which have not yet acquired poly(A) sequences.

RNA initiation with dinucleoside monophosphates during transcription of bacteriophage T4 DNA with RNA polymerase of Escherichia coli

The effects of dinucleoside monophosphates on the transcription of phage T4 DNA by E. coli RNA polymerase have been examined at various concentrations of the sigma subunit and extremely low concentration of ribonucleoside triphosphate. The following conclusions were reached: (i) Labeled specific dinucleoside monophosphates are incorporated as chain initiators. (ii) When the ratio of sigma factor to core enzyme is small, there is a general stimulation by most 5'-guanosyl dinucleoside monophosphates. (iii) When the ratio is increased or holoenzyme is present, ApU, CpA, UpA, and GpU are the most effective stimulators. (iv) At high concentrations of sigma factor, only certain adenosine-containing dinucleoside monophosphates (ApU, CpA, UpA, and ApA) stimulate the reaction. (v) Competition hybridization studies indicate that the RNAs stimulated by dinucleoside monophosphates (ApU, CpA, UpA, and GpU) are of the T4 "early" type. (vi) Studies involving both combinations of stimulatory dinucleoside monophosphates and competitive effects of these compounds on chain initiation by ATP and GTP suggest that the stimulatory dinucleoside monophosphates act as chain initiators and may recognize part of a continuous sequence in a promoter region. Studies based on the incorporation of (3)H-labeled stimulatory dinucleoside monophosphates support the above conclusions.

Replicating, convalently closed, circular DNA from kinetoplasts of Trypanosoma cruzi

When Trypanosoma cruzi are treated with Berenil, a trypanocide, their kinetoplast DNA contains an increased proportion of double-branched circular molecules. These replicating molecules have closed-circular template strands; their decrease in density when complexed by ethidium bromide in a cesium chloride gradient is proportional to the length of the replicated segments. Replication seems to be blocked at specific points, which are equidistantly spaced along the circular kinetoplast DNA molecules. Analysis of about 800 replicating forms showed that the lengths of the replicated branches are not distributed at random, but into several populations, which correspond to multiples of 15% of the total contour length of 0.5 mum. This distribution evokes a discontinuous replication process. The problem of whether kinetoplast DNA is synthesized by successive replication units, or whether and how Berenil might induce specific blocking of DNA replication, is discussed.

Pyrimidine sequences from the DNA of bacteriophages fd, fl, and phi X174

By the use of techniques previously developed to determine the sequence of large, unique pyrimidine oligonucleotides in bacteriophage fd DNA, pyrimidine sequences in the related phage fl and the unrelated phage varphiX174 amber 3 were determined. The DNA of fl contains many pyrimidine sequences completely identical to those in fd, including one sequence of 20 base residues. The large pyrimidine oligonucleotides in varphiX174 DNA are quite different from those in fd, although some homology is observed. There is present in each of the phage DNAs a pyrimidine oligonucleotide rich in thymidine that contains a common sequence of C_T_T_T_T_T_T_T.