Nucleotide Sequence of a Ribonucleic Acid Transcribed in Vitro from λ Phage Deoxyribonucleic Acid

The araC promoter: transcription, mapping and interaction with the araBAD promoter

The start sites of the araC and araBAD gene messenger of E. coli were located by transcription in vitro from short DNA fragments, by high magnification electron microscopy and by genetic mapping. Transcription for these messengers proceeds in opposite directions from the start sites that are 150 base pairs apart. Transcription from the araBAD promoter requires araC protein plus arabinose and CAP protein plus cyclic AMP. In the experiments performed in vitro, inducing the araBAD promoter represses activity of the araC promoter.

In situ hybridization of repetitive monkey genome sequences isolated from defective simian virus 40 DNA

The origin of a repetitive monkey DNA sequence that is incorporated into a defective simian virus 40 genome has been studied. A fragment (about 140 base pairs in length) containing essentially all the repetitive monkey DNA present in the defective and few, if any, SV40 sequences can be cleaved from the purified defective DNA by restriction endonucleases Hind(II and III). Radioactive cRNA prepared with the isolated fragment as template was hybridized in situ to African green monkey chromosomes. The results indicate that all or part of the sequence in question occurs at both centromeric and noncentromeric positions in many, but not all, chromosomes. Of the typical 60 chromosomes, between nine and eleven hybridize with the cRNA in noncentromeric regions.

Doublet frequencies and codon weighting in the DNA of Escherichia coli and its phages

A compilation of nucleic acid sequences from E. coli and its phages has been analysed for the frequency of occurrence of nearest neighbour base doublets and codons. Several statistically significant deviations from random are found in both doublet and codon frequencies. The deviations in E. coli also appear to occur in lambda and in the coat protein gene of MS2, whereas T4 and other parts of the MS2 genome show different sequence properties. These and other findings are discussed in relation to the hypothesis that rapidity of translation of mRNAs in the E. coli system is dependent on doublet frequency and codon usage patterns.

SV40 DNA sequences as an example of the structure of genes functioning in animal cell nuclei

Recent studies of the structure of messenger RNA have demonstrated the existence of untranslated sequences of the 3' and 5' end of the messages. In addition analysis of transcription in vitro has indicated that the nucleotide sequence U6 purine may be part of a transcription termination signal in prokaryotes. Recently it has been possible to determine the sequence of extensive portions of the DNA of SV40 virus. This article reviews the analogies between certain of these sequences and sequences available from prokaryotic messengers and DNAs. Unusual structures, including blocks of AT-rich and GC-rich segment sections and symmetric regions in the DNA near the origin of DNA replication, have been demonstrated and the distribution of stretches of 6 or more deoxyadenylic acids in the DNA of SV40 is consistent with some rho for these sequences in animal cells, either as terminators of transcription or as sites where degradation of transcripts is initiated or sites related to the selective rejection or degradation of transcipts.

Existence and possible roles of transcriptional barriers in T7 DNA early region as shown by electron microscopy

Transcription of T7 DNA in vitro by Escherichia coli RNA polymerase in the absence or presence of termination factor rho has been studied extensively using electron microscopy. It is demonstrated that sequences located between the early genes behave as transient transcriptional barriers in the absence of rho and are recognised both as rho-dependent terminators and as RNaseIII cleavage sites.

Doublet frequencies in sequenced nucleic acids

A doublet frequency count (set of frequencies of the 16 possible two-base sequences) can be calculated from the experimentally determined overall sequence of a nucleic acid. In this paper, a statistical methodology is developed for comparing such counts with random, with others of the same type or with doublet proportions found in whole DNAs. The methods are applied to two major categories of sequenced RNAs. It is found that vertebrate ribosomal and transfer RNAs show significant differences from the overall vertebrate DNA pattern, especially in the frequency of the doublet CG. Bacterial rRNA and tRNA, on the other hand, show less dissimilarity from total DNA. In the RNA of the small bacteriophage MS2, the doublet frequencies of the translated regions of the genome resemble those in the host E. coli, whereas those in the intercistronic regions differ substantially. All these findings are discussed in relation to the origin, evolution and selection of the nucleic acids concerned.

Genetic regulation: the Lac control region

The nucleotide sequence of the lac promoter-operator region has been determined. The 122 base pairs comprising this region include the recognition sites for RNA polymerase, the positive regulatory protein, CAP, and the negative regulatory protein, the repressor. Identification of mutant variants of the sequence combined with the in vitro biochemical studies of others has allowed us to tentatively identify the recognition site for each of these proteins, and to suggest how CAP might act at a distance to affect the interaction of RNA polymerase with the promoter.