Amplification of the DFR1 gene in Saccaromyces cerevisiae

A new system was employed to study amplification of t,he DHF'R gene DFB,1 ) in Sa<,:;charoillYCB§. .Q~~Yi...S!i<;1~. . This system consists of a series of yeast strains containing a casset,te which encodes t he yeast, D..ERl gene ttghtly linked tjO a f usion of the yeast 1EU2. regulat,ory region wi tJ1 the LAQZ str ctural gene from E. cO.1-1 (,) . M. Clement , unpubl i,::;hed) . Th's casset;t e was shown t.o be integrat,ed int o a unj que chromosomal l ocati on in each strain . Yeast cells were se l ected for MTX-resistance and overproduction of ~ galac t osi d se ( B-gal ). Since the inserted DF'Rl and ~ACZ genes are independently regulated, it was thought that cel l s with this phenotype probably contain e d ampl if ications of the cassette. A lar ge variat ion in the f requn y o f MTX-resistance was found between the di ff e r ent str ains. These freqlen c ~ es r anged from about 2 x 10 - 7 fo r a population of cells containing the cassette integrated at, the BI J2.l gene in t,he middle of the long arm of chromosome V, to about 5 x 10-4 for a strain with the cassette i nserted in the r DNA cluster Abo It 85% of the MTX- res i stcmt iso l ates examined showed enhanced B·-gal act i v ity rel a t ive t o the parental strain . For the ma jorit y of strains, the mean B- gal activity in drug-r sistant clones was about 3 times that o f the parent following a single se l ect i on step . I n con t r ast, primary MTX-resistant derivat~ves of cells with the cassette inserted 3 at the rDNA cluster showed inc r eases in B- gal activity ranging from 9 - 14 f old r elative to the parent. Analysis of the latte r s train by Southe rn hybr idization indicated that the cassette was inde e d amplified several fold in MTX-re sistant derivatives. A sing l e strain, in which the cassette was inserted at the !lEA;], loc u.s , was used to examine in more detai 1 , the parameters affecting DFRl gene amplificat~ion in yeast . The mean B- gal activity in drug-resistant derivatives of this strain could be increased from 3 to 6 or 7 fold relative to the parent, by stepwise sel ection using increasing MTX concentrations. B-gal overproduction was found to be un stable in all primary and highly -resistant isolates examined. There was no indication, h owever, of a decrease i n growth r a t e in MTX-res i s tant cells which overproduced B - gal.

Macroeconomic News and LOB in Foreign Exchange ECN Market

We investigate the macroeconomic news effect on the dynamics of the limit order books (LOB) for euro-dollar ECN market in different economic states between Jan. 2006 to Dec. 2009. Using a VAR-STR model on the news surprise, pure news, aggregated good and bad news, we show that news effects on the LOB dynamics vary in different states of economy. The LOB dynamics are measured by depth, spread, slope and volatility. In contract to slope and volatility, depth and spread strongly respond to news surprise and pure news during recession and expansion. These characteristics are more affected by aggregated good and bad news during expansion. News effects are robust to alternative characteristic measures, the different sides of the LOB and the different levels in the LOB.