Gerard Zurawski

Chloroplast DNA and the Study of Plant Phylogeny: Present Status and Future Prospects

More than a quarter of a century has passed since the publication of Zuckerkandl and Pauling’s (1965) seminal article on the evolutionary implications of macromolecular sequence data. Two fundamental suggestions were made in that article: first, Zuckerkandl and Pauling pointed out that molecular change (nucleotide or amino acid substitutions) might occur at a rate that is proportional to clock time (the molecular clock hypothesis); and second, they noted that the topology of evolutionary branchings (phylogenies) could be deduced from the pattern of molecular change. These two related suggestions form the theoretical underpinnings of the science of molecular evolution.

Structure and regulation of aroH, the structural gene for the tryptophan-repressible 3-deoxy-d-arabino-heptulosonic acid-7-phosphate synthetase of Escherichia coli☆

Abstract The structural gene for the tryptophan-repressible 3-deoxy- d -arabino-heptulosonic acid-7-phosphate synthetase of Escherichia coli, aroH, has been cloned and partially sequenced. The translation start site and presumed translation stop site were identified by amino acid sequence analyses with aroH protein synthesized in vitro. Transcription in vitro is initiated at either of two start sites, three base-pairs apart. Although the transcription start sites are located approximately 120 base-pairs before the translation start site, there does not appear to be a site of transcription termination in the leader region. Regulatory studies performed in vivo support this conclusion and suggest that repression may be the sole specific regulatory mechanism used to control expression of this single gene operon. RNA polymerase and trp repressor bind at the −35 region of the aroH promoter, in a region homologous to the operator of the trp operon. Since the trp operon operator overlaps the −10 but not the −35 region of the trp promoter, it appears that trp repressor inhibits transcription initiation in the two operons by binding to different RNA polymerase recognition regions in the respective promoters.

Evolutionary Relationships of the Caryophyllidae Based on Comparative rbcL Sequences

In the long-standing controversy over the Centrospermae (i.e., Caryophyllales) and putatively related orders, comparative sequencing of the chloroplast gene, ribulose-1,5-bisphosphate carboxylase, large subunit (rbcL), shows that the Polygonales and Plumbaginales are not closely related to the Caryophyllales as has been hypothesized, nor are they related to members of the Dilleniidae. The sequence data supports the assignment of independent superorder status to the Caryophyllales and the Polygonales and Plumbaginales. These sequence data further suggest early and independent paths of evolution for the Polygonales and Plumbaginales, and the Caryophyllales.

Escherichia coli tryptophan operon leader mutations, which relieve transcription termination, are cis-dominant to trp leader mutations, which increase transcription termination☆

Abstract Strains with increased expression of the Escherichia coli trp operon were selected from trp leader mutants, which have decreased trp operon expression. The trp leader nucleotide sequences of 22 mutant strains with trp operon-linked mutations were determined. The strains were shown to be either true revertants or to have secondary site mutations in the trp leader region. All the secondary site mutations were located immediately proximal to the transcription termination site and overlapped with previously identified single base-pair mutations, which relieve transcription termination.

In vivo cloning of DNA regions carrying mutations linked to selectable genes: Application to mutations in the regulatory region of the Escherichia coli tryptophan operon

Abstract A rapid method for cloning DNA regions carrying specific mutations onto a previously characterized plasmid is described. This method is used to clone DNA regions carrying trpL or trpP mutations in the Escherichia coli tryptophan operon. The applicability of the method for other systems is discussed.