Circles: The replication-recombination-chromosome segregation connection

Crossing over by homologous recombination between monomeric circular chromosomes generates dimeric circular chromosomes that cannot be segregated to daughter cells during cell division. In Escherichia coli, homologous recombination is biased so that most homologous recombination events generate noncrossover monomeric circular chromosomes. This bias is lost in ruv mutants. A novel protein, RarA, which is highly conserved in eubacteria and eukaryotes and is related to the RuvB and the DnaX proteins, γ and τ, may influence the formation of crossover recombinants. Those dimeric chromosomes that do form are converted to monomers by Xer site-specific recombination at the recombination site dif, located in the replication terminus region of the E. coli chromosome. The septum-located FtsK protein, which coordinates cell division with chromosome segregation, is required for a complete Xer recombination reaction at dif. Only correctly positioned dif sites present in a chromosomal dimer are able to access septum-located FtsK. FtsK acts by facilitating a conformational change in the Xer recombination Holliday junction intermediate formed by XerC recombinase. This change provides a substrate for XerD, which then completes the recombination reaction.

Rolling replication of short DNA circles.

Natural genes and proteins often contain tandemly repeated sequence motifs that dramatically increase physiological specificity and activity. Given the selective value of such repeats, it is likely that several different mechanisms have been responsible for their generation. One mechanism that has been shown to generate relatively long tandem repeats (in the kilobase range) is rolling circle replication. In this communication, we demonstrate that rolling circle synthesis in a simple enzymatic system can produce tandem repeats of monomers as short as 34 bp. In addition to suggesting possible origins for natural tandem repeats, these observations provide a facile means for constructing libraries of repeated motifs for use in "in vitro evolution" experiments designed to select molecules with defined biological or chemical properties.

Handbook of the freshwater fishes of India : giving the characteristic peculiarities of all the species at present known, and intended as a guide to students and district officers / By R. Beavan.

[Incomplete]

Printed form letter giving rules for suspended students,

This document is signed by John T. Kirkland.

EU-Turkey Relations: Turning vicious circles into virtuous ones. CEPS Policy Brief No. 317, 26 March 2014

The coming weeks and months will be decisive for the general tenor of politics in Turkey. The country faces local elections this March, presidential elections in August and general elections next June, while top-level political scandals compound the deterioration in the state of democracy and rule of law. At the same time, stagnation in Turkey’s accession process continues to sour relations with the EU. In this new Policy Brief, Steven Blockmans puts forward a number of recommendations to help drive the EU accession process forward, namely the early opening of negotiation chapters 23 (judiciary and fundamental rights) and 24 (justice, freedom and security), in line with the EU’s so-called New Approach. In that way reform could not just be assured on paper, but a track record in implementation could be established throughout the process. To achieve this, member states, and Cyprus in particular, need to be persuaded to end their opposition to formulating benchmarks for the opening of accession negotiating chapters 23 and 24.