Comparison of the nucleotide sequences of the initial transcribed regions of the tryptophan operons of Escherichia coli and Salmonella typhimurium

Structural and physiological studies of the Escherichia coli histidine operon inserted into plasmid vectors

A fragment of deoxyribonucleic acid 5,300 base paris long and containing the promoter-proximal portion of the histidine operon of Escherichia coli K-12, has been cloned in plasmid pBR313 (plasmids pCB2 and pCB3). Restriction mapping, partial nucleotide sequencing, and studies on functional expression in vivo and on protein synthesis in minicells have shown that the fragment contains the regulatory region of the operon, the hisG, hisD genes, and part of the hisC gene. Another plasmid (pCB5) contained the hisG gene and part of the hisD gene. Expression of the hisG gene in the latter plasmid was under control of the tetracycline promoter of the pBR313 plasmid. The in vivo expression of the two groups of plasmids described above, as well as their effect on the expression of the histidine genes not carried by the plasmids but present on the host chromosome, has been studied. The presence of multiple copies of pCB2 or pCB3, but not of pCB5, prevented derepression of the chromosomal histidine operon. Possible interpretations of this phenomenon are discussed.

The construction and characterisation of plasmid vectors suitable for the expression of all DNA phases under the control of the E. coli tryptophan promoter

A DNA fragment flanked in the E. coli genome by Hinf I sites and containing the E. coli tryptophan promoter-operator and nucleotides specifying the leader sequence and first seven amino acids of trp E, has been cloned in the Hind III site of pBR322 with the aid of Hind III linkers. The Hind III site upstream from the trp promoter in the transcriptional sense was deleted to generate a Hind III cloning vector, designated pWT111, suitable for the expression of cloned DNA sequences as fusion products. Derivatives of this plasmid were constructed, designated pWT121 and pWT131, whose Hind III cloning sites differ with respect to their translation phasing relative to the initiator ATG of the trp E gene. Both pWT121 and pWT131 have a higher copy number per cell than pWT111. The tetracycline genes of all three plasmids are under trp promoter control and could be used to monitor the transcription of foreign genes inserted at the Hind III site of the vectors.

Influenza antigenic determinants are expressed from haemagglutinin genes cloned in Escherichia coli

A gene sequence for the fowl plague virus (FPV) haemagglutinin molecule has been inserted into a bacterial plasmid such that its transcription is under the control of a promoter derived from the tryptophan operon. Such plasmids direct the synthesis of a protein that reacts specifically with antisera to FPV haemagglutinin. Evidence is also presented that in some cases DNA inserted at the HindIII site of pBR322 is expressed.

Comparative studies on the regulation of tryptophan synthesis

In vitro DNA recombination techniques have revolutionized the study of genetic control of biosynthetic pathways. Using examples drawn from the pathway of tryptophan synthesis, approaches to the deciphering of regulatory signals and response mechanisms through transposition of DNA segments and DNA sequence analysis will be presented. After reviewing the known chromosomal arrangements and regulatory patterns of trp genes in the bacterial groups studied so far, and describing the results of transferring all or part of the pathway's genes from one organism to a distantly related one, the use of this technique to analyze new organisms will be described. Along with some advantages over the conventional methods there are some pitfalls. Finally, since it is likely that events analogous to recombinant DNA experiments take place readily in nature, their consequences in studies of bacterial evolution will be conjectured.

The structure of a transcriptional unit on colicin E1 plasmid

In an RNA-synthesizing system in vitro, a low-molecular-weight RNA consisting of about 110 residues (RNA-I) was efficiently synthesized on DNA of colicin E 1 plasmid (ColE1) and its deletion derivatives. The promoter site for RNA-I was analysed by testing the RNA polymerase-binding ability and template activity of restriction fragments; it was mapped in the region between the replication initiation site and the colicin immunity gene of ColE1. The direction of transcription was determined by hybridization tests to the separated strands of the template. The DNA region directing RNA-I was sequenced, and RNA-I was assigned on the sequence based on the nearest-neighbour data of RNA. The sequences of its promoter and terminator regions were also deduced. Although the function of this small RNA species is unknown, a unique secondary structure could be constructed from its sequence and sensitivity to RNase.

The regulatory region of the trp operon of Serratia marcescens

The nucleotide sequence of the regulatory region of the trp operon of Serratia marcescens is presented. It contains a transcription termination control site in the transcribed leader region preceding the first structural gene of the operon as well as a regulated promoter/operator transcription initiation region. The structural organisation of the leader region differs substantially from that of Escherichia coli.