Studies on the binding of actinomycin D to DNA and DNA model polymers

RNA-DNA covalent bonds between the RNA primers and the DNA products formed by RNA tumor virus DNA polymerase

Initiation of DNA synthesis by endogenous RNA primer molecules was studied with three different RNA tumor viruses. The influence of the method of virus disruption on the observed RNA-DNA bonds was ascertained. Ether disrupted virions of both murine leukemia virus (MuLV) and the B77 strain of avian sarcoma virus (B77 virus) have rC-dC and rA-dA covalent linkages between RNA primers and newly synthesized DNA. None of the 14 other possible bonds were formed. Ether-disrupted virions of avian myeloblastosis virus (AMV) have rU-dC and rA-dA linkages. In contrast, work reported herein and from other laboratories shows that Nonidet P-40 (NP-40)-disrupted virions of all three viruses have only the rA-dA junction. Studies with virus particles which were first disrupted with ether and then treated with NP-40 indicated that the detergent treatment disallowed the formation of the ribopyrimidine-dC internucleotide bond. The same transfers are found with AMV in the presence or absence of actinomycin D, where only single-stranded DNA is formed. This finding is consistent with the notion that virtually all of the significant primers have been recognized. In contrast to mature virions, transfer experiments with ether-disrupted early harvest (5 min) MuLV showed only the rC-dC bond; the rA-dA bond was absent. The short-time harvest contains a significantly higher proportion of infectious virions than 24-h harvests. Also, since the RNA from early harvest virus is appreciably more homogenous than the RNA of mature MuLV, it is concluded that the ribopyrimidine-dC linkage is the more significant initiation event from a biochemical standpoint.

Ribonucleic acid and protein synthesis during germination of Myxococcus xanthus myxospores

Ribonucleic acid (RNA) and protein synthesis during myxospore germination were examined. When RNA synthesis was inhibited more than 90% by either actinomycin D (Act D) or rifampin, germination was prevented. The data were consistent with the interpretation that rifampin did not interfere with protein synthesis in any way other than by inhibition of messenger RNA formation. Act D concentrations as high as 20 mug/ml did not totally inhibit RNA synthesis. In the presence of 8 mug of Act D/ml, germinating myxospores synthesized transfer RNA, 16S RNA, and 23S RNA. Evidence was presented which indicated that messenger RNA was also synthesized early in the germination period both in the presence and absence of 8 mug of Act D/ml. One explanation for the escape synthesis of RNA in germinating myxospores is that Act D exerts a differential effect on the transcription of larger versus smaller cistrons, the latter having a lower probability of binding Act D. We have found that in the presence of 8 mug of Act D/ml, escape RNA synthesis in myxospores was 25% for 23S RNA, 55% for 16S RNA, and more than 90% for 4S RNA. We have shown that germination of myxospores requires both RNA and protein synthesis during the first 25 to 35 min in germination medium. This finding does not support the earlier suggestion by Ramsey and Dworkin that a stable germination messenger RNA is required for germination of the myxospores of Myxococcus xanthus.

A transcribing activity induced by satellite phage P4

Satellite bacteriophage P4 induces a new transcribing enzyme that synthesizes polyriboguanylic acid in the presence of the poly(dG).poly(dC) homopolymer pair. This transcribing activity was partially purified and shown to be distinct from the host RNA polymerase. Analysis of conditional lethal mutants suggests that this new enzyme is necessary for replication of phage DNA.

Association of actinomycin D and deoxyribodinucleotides as a model for binding of the drug to DNA

The association of actinomycin D and eleven different deoxyribodinucleotides were studied as model complexes for the interaction of actinomycin D and DNA. All of the deoxyribodinucleotides containing guanine will complex with actinomycin D, and the guanine base has a preferred orientation with respect to the chromophore of actinomycin D. The spectrophotometric binding curve for pdG-dC is sigmoidal (Hill constant = 2.0 +/- 0.2), while the binding curves of all other dinucleotides of the form pdN-dG are hyperbolic. The equilibrium expression for the complex with pdG-dC was second order in dinucleotide concentration, with K(App) = 1.7 x 10(7) liter(2)/mol(2), while the binding of pdC-dG was first order in dinucleotide concentration, with K(App) 1.8 x 10(3) liter/mol. The sigmoidal pdG-dC binding curve shows that actinomycin D has a preference for G-C sequences of DNA as potential binding sites.

Ribosomal RNA synthesis in vitro: a protein-DNA complex from Bacillus subtilis active in initiation of transcription

A protein-DNA transcription complex, isolated from logarithmic-phase cells of Bacillus subtilis, is active in the initiation of new rounds of RNA synthesis in vitro. Transcription directed by the endogenous DNA of the complex is sensitive to inhibitors of initiation. In addition, the effect of addition of a competing template indicates that RNA polymerase in the complex is bound to endogenous DNA in a dissociable, preinitiation state. Hybridization-competition analysis of the RNA product obtained from the in vitro reaction indicates that it is greatly enriched for ribosomal RNA sequences. This initiating complex should be useful for the study of regulation of expression of ribosomal RNA genes.

Lac repressor binding to synthetic DNAs of defined nucleotide sequence

Binding of lac repressor to 20 synthetic DNAs of high molecular weight with defined repeating sequences was investigated by competition experiments. Although none of these DNAs binds repressor as tightly as does lac operator, most do bind to a measurable extent. Their affinity for repressor varies greatly and is a function of both nucleotide composition and sequence. Poly(dC-dC).poly(dG-dC) competes for repressor 200-times less well than either poly(dA-dT).poly(dA-dT) or poly(dT-dT-dG).poly(dC-dA-dA). The other DNAs show a broad spectrum of affinities for repressor between these extremes. These results show that the lac repressor has affinity for, and can distinguish between, sequences distantly related to its operator.